Voyager Therapeutics (VYGR) 10-K 28 Feb 24 2023 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Feb. 21, 2024	Jun. 30, 2023
Document and Entity Information
Document Type	10-K
Document Annual Report	true
Document Transition Report	false
Document Period End Date	Dec. 31, 2023
Entity File Number	001-37625
Entity Registrant Name	Voyager Therapeutics, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	46-3003182
Entity Address, Address Line One	75 Hayden Avenue
Entity Address, City or Town	Lexington
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02421
City Area Code	857
Local Phone Number	259-5340
Title of 12(b) Security	Common Stock, $0.001 par value
Trading Symbol	VYGR
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Document Financial Statement Error Correction [Flag]	false
Entity Shell Company	false
Entity Central Index Key	0001640266
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	FY
Entity Public Float			$ 488.8
Entity Common Stock, Shares Outstanding		54,300,627
Auditor Name	Ernst & Young LLP
Auditor Firm ID	42
Auditor Location	Boston, Massachusetts

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 68,802	$ 98,959
Marketable securities	162,073	19,889
Accounts receivable	80,150
Related party collaboration receivable	3,341	257
Prepaid expenses and other current assets	5,318	5,394
Total current assets	319,684	124,499
Property and equipment, net	16,494	17,857
Deposits and other non-current assets	1,593	1,515
Operating lease, right-of-use assets	13,510	15,485
Total assets	351,281	159,356
Current liabilities:
Accounts payable	1,604	2,566
Accrued expenses	16,823	7,816
Other current liabilities	3,200	2,832
Deferred revenue, current	42,881	59,377
Total current liabilities	64,508	72,591
Deferred revenue, non-current	32,359	6,450
Other non-current liabilities	18,094	21,295
Total liabilities	114,961	100,336
Commitments, contingencies, and other liabilities (see note 8)
Stockholders' equity:
Preferred stock, $0.001 par value: 5,000,000 shares authorized; no shares issued and outstanding at December 31, 2023 and 2022
Common stock, $0.001 par value: 120,000,000 shares authorized; 44,038,333 and 38,613,891 shares issued and outstanding at December 31, 2023 and 2022, respectively	44	38
Additional paid-in capital	497,506	452,713
Accumulated other comprehensive loss	(48)	(219)
Accumulated deficit	(261,182)	(393,512)
Total stockholders' equity	236,320	59,020
Total liabilities and stockholders' equity	$ 351,281	$ 159,356

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2023	Dec. 31, 2022
Consolidated Balance Sheets
Preferred Stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred Stock, Shares Authorized	5,000,000	5,000,000
Preferred Stock, Shares Issued	0	0
Preferred Stock, Shares Outstanding	0	0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common Stock, Shares Authorized	120,000,000	120,000,000
Common Stock, Shares, Issued	44,038,333	38,613,891
Common Stock, Shares, Outstanding	44,038,333	38,613,891

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Income (Loss) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Consolidated Statements of Operations and Comprehensive Income (Loss)
Collaboration revenue	$ 250,008	$ 40,907	$ 37,415
Operating expenses:
Research and development	92,172	60,764	73,787
General and administrative	35,822	30,980	37,246
Total operating expenses	127,994	91,744	111,033
Operating income (loss)	122,014	(50,837)	(73,618)
Other income, net:
Interest income (expense)	11,721	1,792	(390)
Other income	3	2,653	2,811
Total other income, net	11,724	4,445	2,421
Income (loss) before income taxes	133,738	(46,392)	(71,197)
Income tax provision	1,408	16
Net income (loss)	132,330	(46,408)	(71,197)
Other comprehensive income (loss)
Net unrealized gain (loss) on available-for-sale-securities	171	(81)	(4)
Total other comprehensive income (loss)	171	(81)	(4)
Comprehensive income (loss)	$ 132,501	$ (46,489)	$ (71,201)
Net income (loss) per share, basic	$ 3.08	$ (1.21)	$ (1.89)
Net income (loss) per share, diluted	$ 2.97	$ (1.21)	$ (1.89)
Weighted-average common shares outstanding, basic	43,020,747	38,356,810	37,668,947
Weighted-average common shares outstanding, diluted	44,569,334	38,356,810	37,668,947

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit	Total
Stockholders' Equity, Beginning Balance at Dec. 31, 2020	$ 37	$ 430,324	$ (134)	$ (275,907)	$ 154,320
Shares, Outstanding, Beginning Balance at Dec. 31, 2020	37,368,027
Exercises of vested stock options	$ 1	27			28
Exercises of vested stock options (in shares)	3,811
Vesting of restricted stock units (in shares)	346,551
Issuance of common stock under ESPP		918			918
Issuance of common stock under ESPP (in shares)	200,006
Stock based compensation expense		10,990			10,990
Unrealized gain (loss) on available-for-sale securities, net of tax			(4)		(4)
Net income (loss)				(71,197)	(71,197)
Stockholders' Equity, Ending Balance at Dec. 31, 2021	$ 38	442,259	(138)	(347,104)	95,055
Shares, Outstanding, Ending Balance at Dec. 31, 2021	37,918,395
Exercises of vested stock options		629			629
Exercises of vested stock options (in shares)	89,012
Vesting of restricted stock units (in shares)	456,219
Issuance of common stock under ESPP		672			672
Issuance of common stock under ESPP (in shares)	150,265
Stock based compensation expense		9,153			9,153
Unrealized gain (loss) on available-for-sale securities, net of tax			(81)		(81)
Net income (loss)				(46,408)	(46,408)
Stockholders' Equity, Ending Balance at Dec. 31, 2022	$ 38	452,713	(219)	(393,512)	59,020
Shares, Outstanding, Ending Balance at Dec. 31, 2022	38,613,891
Exercises of vested stock options	$ 1	1,851			$ 1,852
Exercises of vested stock options (in shares)	385,655				385,655
Vesting of restricted stock units (in shares)	531,560
Issuance of common stock in connection with the 2023 Neurocrine Collaboration Agreement	$ 5	31,116			$ 31,121
Issuance of common stock in connection with the 2023 Neurocrine Collaboration Agreement (in shares)	4,395,588
Issuance of common stock under ESPP		959			959
Issuance of common stock under ESPP (in shares)	111,639
Stock based compensation expense		10,867			10,867
Unrealized gain (loss) on available-for-sale securities, net of tax			171		171
Net income (loss)				132,330	132,330
Stockholders' Equity, Ending Balance at Dec. 31, 2023	$ 44	$ 497,506	$ (48)	$ (261,182)	$ 236,320
Shares, Outstanding, Ending Balance at Dec. 31, 2023	44,038,333

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Cash flow from operating activities
Net income (loss)	$ 132,330	$ (46,408)	$ (71,197)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Stock-based compensation expense	11,153	9,344	11,324
Depreciation	4,441	6,191	5,165
Amortization of premiums and discounts on marketable securities	(3,626)	(16)	349
Gain on lease termination		(2,468)
Change in fair value of common stock and warrants to purchase equity securities			(2,460)
Loss on disposal of fixed assets	178	377
Changes in operating assets and liabilities:
Accounts receivable	(80,150)
Related party collaboration receivable	(3,084)	475	7,280
Prepaid expenses and other assets	76	(1,967)	1,883
Operating lease, right-of-use assets	1,975	3,462	2,606
Other non-current assets		(152)	69
Accounts payable	(962)	1,992	(60)
Accrued expenses	9,007	(3,148)	(3,335)
Operating lease liabilities	(2,833)	(3,922)	(3,428)
Deferred revenue	9,414	23,731	(1,721)
Net cash provided by (used in) operating activities	77,919	(12,509)	(53,525)
Cash flow from investing activities
Purchases of property and equipment	(3,256)	(2,491)	(1,609)
Purchases of marketable securities	(223,968)	(54,848)	(15,117)
Proceeds from sales and maturities of marketable securities	85,581	50,000	82,632
Net cash (used in) provided by investing activities	(141,643)	(7,339)	65,906
Cash flow from financing activities
Proceeds from the exercise of stock options	1,852	629	28
Proceeds from the issuance of common stock in connection with the 2023 Neurocrine Collaboration Agreement	31,121
Proceeds from the purchase of common stock under ESPP	672	481	584
Net cash provided by financing activities	33,645	1,110	612
Net (decrease) increase in cash and cash equivalents	(30,079)	(18,738)	12,993
Cash, cash equivalents, and restricted cash beginning of period	100,474	119,212	106,219
Cash, cash equivalents, and restricted cash end of period	$ 70,395	100,474	119,212
Supplemental disclosure of cash and non-cash activities
Operating lease right-of-use assets obtained in exchange for operating lease liabilities			664
Capital expenditures incurred but not yet paid		$ 14	$ 80

Nature of business

Nature of business	12 Months Ended
	Dec. 31, 2023
Nature of business
Nature of business	​ 1. Nature of business Voyager Therapeutics, Inc. (the “Company”) is a biotechnology company whose mission is to leverage the power of human genetics to modify the course of and ultimately cure neurological diseases. The Company’s pipeline includes programs for Alzheimer’s disease (“AD”); amyotrophic lateral sclerosis (“ALS”); Parkinson’s disease, and multiple other diseases of the central nervous system, (“CNS”). Many of the Company’s programs are derived from its TRACER™ adeno-associated virus (“AAV”) capsid discovery platform, which the Company has used to generate novel capsids (“TRACER Capsids”) and identify associated receptors to potentially enable high brain penetration with genetic medicines following intravenous dosing. Some of the Company’s programs are wholly-owned, and some are advancing with licensees and collaborators including Alexion, AstraZeneca Rare Disease (“Alexion”); Novartis Pharma AG, (“Novartis”); Neurocrine Biosciences, Inc. (“Neurocrine”); and Sangamo Therapeutics, Inc. (“Sangamo”). ​ The Company focuses on leveraging its expertise in capsid discovery and neuropharmacology to address the delivery hurdles that have constrained the genetic medicine and neurology disciplines, with the goal of either halting or slowing disease progression or reducing symptom severity, and therefore providing clinically meaningful impact to patients. The Company is advancing its own proprietary pipeline of drug candidates for neurological diseases, with a focus on AD. The Company’s wholly-owned prioritized pipeline programs include an anti-tau antibody for AD; a superoxide dismutase 1 (“SOD1”) silencing gene therapy for ALS; and a tau silencing gene therapy for AD. The Company identified a lead development candidate for its anti-tau antibody program in the first quarter of 2023, initiated good laboratory practices (“GLP”) toxicology studies in the third quarter of 2023, and expects to submit an investigational new drug (“IND”), application to the U.S. Food and Drug Administration (“FDA”) for this program in the first half of 2024. The Company believes this trial could result in the potential to generate proof-of-concept data for slowing the spread of pathological tau via tau positron emission tomography imaging in 2026. The Company identified a lead development candidate for its SOD1 silencing gene therapy program in the fourth quarter of 2023, and the Company expects to submit the IND application for its SOD1 silencing gene therapy program in mid-2025. The Company promoted its tau silencing gene therapy program to a prioritized program in the first quarter of 2024, based on preclinical data demonstrating robust reductions in tau messenger RNA (“mRNA”) in a murine model, and it anticipates submission of an IND in 2026. The Company’s proprietary pipeline also includes an early research initiative to develop a gene therapy for the treatment of AD. This program seeks to combine a vectorized anti-amyloid antibody with a TRACER Capsid. ​ The Company is also working with its collaboration partners on multiple programs. In January 2019 and January 2023, the Company entered into collaboration and license agreements with Neurocrine. Under the agreements with Neurocrine, the Company is actively advancing two later preclinical stage programs: a glucocerebrosidase 1 (“GBA1”) gene therapy program for Parkinson’s disease and other GBA1-mediated diseases, and a frataxin gene therapy program for Friedreich’s ataxia (the “FA Program”). Pursuant to such agreements, the Company is also working with Neurocrine on five early-stage programs for the research, development, manufacture and commercialization of gene therapies designed to address CNS diseases or conditions associated with rare genetic targets. The Company has also entered into agreements with licensees including Novartis, Alexion, and Sangamo, to license or to provide options to receive exclusive licenses to certain TRACER Capsids. As described further below, in December 2023, the Company entered into a license and collaboration agreement with Novartis to provide Novartis certain rights regarding the development of potential gene therapy product candidates for the treatment of spinal muscular atrophy and to collaborate with Novartis to develop gene therapy product candidates for the treatment of Huntington’s disease. The joint steering committee with Neurocrine selected a development candidate for the FA Program, during the first quarter of 2024, and expects to advance into first-in-human clinical trials in 2025. The Company also anticipates that its collaborative partners and licensees will submit at least one additional IND application for a partnered program and initiate clinical development for the associated program by the end of 2025. ​ The Company has a history of incurring annual net operating losses prior to the operating income in 2023. As of December 31, 2023, the Company had an accumulated deficit of $261.2 million. The Company has not generated any product revenue and has financed its operations primarily through public offerings and private placements of its equity securities and funding from fees, milestone payments, and cost reimbursements associated with its prior and current collaborations and license agreements. ​ As of December 31, 2023, the Company had cash, cash equivalents, and marketable securities of $230.9 million. Based upon its current operating plan, the Company expects that its existing cash, cash equivalents, and marketable securities at December 31, 2023, together with the upfront $80.0 million payment received in January 2024 in connection with the Collaboration and License Agreement by and between the Company and Novartis dated as of December 28, 2023 (the “2023 Novartis Collaboration Agreement”), $20.0 million in proceeds from Novartis’ equity purchase, and $93.5 million in net proceeds received from a public offering closed in January 2024, to be sufficient to meet the Company’s planned operating expenses and capital expenditure requirements for at least twelve months from the issuance of these consolidated financial statements. ​ There can be no assurance that the Company will be able to obtain additional debt or equity financing on terms acceptable to the Company or generate product revenue or revenue from collaboration partners, on a timely basis or at all. The failure of the Company to obtain sufficient funds on acceptable terms when needed could have a material adverse effect on the Company’s business, results of operations, and financial condition. ​

Summary of significant accounti

Summary of significant accounting policies and basis of presentation	12 Months Ended
	Dec. 31, 2023
Summary of significant accounting policies and basis of presentation
Summary of significant accounting policies and basis of presentation	2. Summary of significant accounting policies and basis of presentation Basis of presentation ​ The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”) and pursuant to the rules and regulations of the U.S. Securities and Exchange Commission (“SEC”) for reporting on Form 10-K. The Company’s consolidated financial statements include the accounts of Voyager Therapeutics, Inc. and its wholly-owned subsidiary, Voyager Securities Corporation. All intercompany balances and transactions have been eliminated. ​ Use of Estimates ​ The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. On an ongoing basis, the Company’s management evaluates its estimates, which include, but are not limited to, estimates related to revenue recognition, research and development accrued expenses, stock-based compensation expense, and income taxes. The Company bases its estimates on historical experience and other market specific or other relevant assumptions that it believes to be reasonable under the circumstances. Actual results may differ from those estimates or assumptions. ​ Fair Value of Financial Instruments ​ ASC Topic 820, Fair Value Measurement ​ ASC 820 identifies fair value as the exchange price, or exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As a basis for considering market participant assumptions in fair value measurements, ASC 820 establishes a three-tier fair value hierarchy that distinguishes between the following: ​ ● Level 1 —Quoted market prices in active markets for identical assets or liabilities. ● Level 2 —Inputs other than Level 1 inputs that are either directly or indirectly observable, such as quoted market prices, interest rates, and yield curves. ● Level 3 —Unobservable inputs developed using estimates of assumptions developed by the Company, which reflect those that a market participant would use. ​ To the extent that the valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. ​ The carrying amounts reflected in the balance sheets for cash and cash equivalents, prepaid expenses and other current assets, accounts payable and accrued expenses approximate their fair values, due to their short-term nature. ​ Cash and Cash Equivalents ​ The Company considers all highly liquid investments purchased with original maturities of 90 days or less at acquisition to be cash equivalents. Cash and cash equivalents include cash held in banks and amounts held in money market funds. ​ Marketable Securities ​ The Company classifies marketable securities with a remaining maturity of greater than three months when purchased as available-for-sale. Marketable securities with a remaining maturity date greater than one year are classified as non-current where the Company has the intent and ability to hold these securities for at least the next 12 months. ​ All available-for-sale debt securities are carried at fair value with the unrealized gains and losses included in other comprehensive income (loss) as a component of stockholders’ equity until realized. Any premium or discount arising at purchase is amortized and/or accreted to interest income and/or expense. Realized gains and losses are determined using the specific identification method and are included in other income. If any adjustment to fair value reflects a decline in value of the investment, the Company uses a forward-looking approach based on expected losses to estimate credit losses on certain types of financial instruments, including trade receivables and available-for-sale debt securities. No other than temporary losses or credit losses have been recognized. ​ Cash, cash equivalents, and marketable securities as of December 31, 2023 and 2022 consist of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Amortized ​ Unrealized ​ Unrealized ​ Fair ​ Cost Gains Losses Value ​ ​ (in thousands) As of December 31, 2023 ​ ​ ​ ​ ​ ​ Money market funds included in cash and cash equivalents $ 65,589 ​ ​ — ​ ​ — ​ $ 65,589 ​ Marketable securities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ U.S. Treasury notes ​ ​ 102,966 ​ ​ 81 ​ ​ (3) ​ ​ 103,044 ​ U.S. Government agency securities ​ ​ 31,068 ​ ​ 10 ​ ​ (3) ​ ​ 31,075 ​ Corporate bonds ​ ​ 23,975 ​ ​ 2 ​ ​ (7) ​ ​ 23,970 ​ Commercial paper ​ ​ 3,985 ​ ​ — ​ ​ — ​ ​ 3,985 ​ Total money market funds and marketable securities $ 227,583 ​ $ 93 ​ $ (13) ​ $ 227,663 ​ As of December 31, 2022 ​ ​ ​ ​ ​ Money market funds included in cash and cash equivalents $ 91,724 ​ $ — ​ $ — ​ $ 91,724 ​ Marketable securities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ U.S. Treasury notes ​ 19,980 ​ ​ — ​ ​ (91) ​ ​ 19,889 ​ Total money market funds and marketable securities $ 111,704 ​ $ — ​ $ (91) ​ $ 111,613 ​ ​ All of the Company’s marketable securities at December 31, 2023 and 2022 have a contractual maturity of one year or less. ​ The Company reviews investments whenever the fair value of an investment is less than the amortized cost and evidence indicates that an investment’s carrying amount is not recoverable within a reasonable period of time. In connection with these investments, the Company evaluates whether the decline in fair value has resulted from credit losses or other factors, considering the extent to which fair value is less than amortized cost, any changes to the rating of the security by a rating agency, and adverse conditions specifically related to the security, among other factors. If this assessment indicates that a credit loss exists, the present value of cash flows expected to be collected from the security is compared to the amortized cost basis of the security. If the present value of cash flows expected to be collected is less than the amortized cost basis, a credit loss exists and an allowance for credit losses is recorded for the credit loss on the condensed consolidated balance sheet, limited by the amount that the fair value is less than the amortized cost basis. Any impairment that is not related to credit is recognized in other comprehensive income (loss). Changes in the allowance for credit losses are recorded as a provision for (or reversal of) credit loss expense in general and administrative expenses within the consolidated statement of operations and comprehensive income (loss). Losses are charged against the allowance when the Company believes the uncollectability of an available-for-sale security is confirmed or when either of the criteria regarding intent or requirement to sell is met. ​ The Company held $44.2 million and $19.9 million in marketable securities that were in an unrealized loss position as of December 31, 2023 and December 31, 2022, respectively. The unrealized losses at December 31, 2023 and December 31, 2022 were attributable to changes in interest rates and the unrealized losses do not represent credit losses. The Company does not intend to sell these securities and it is not more likely than not that it will be required to sell them before recovery of their amortized cost basis. ​ Restricted Cash ​ As of December 31, 2023 and 2022, the Company maintained restricted cash totaling approximately $1.6 million and $1.5 million, respectively, held in the form of money market accounts as collateral for the Company’s facility lease obligations. The balance is included within deposits and other non-current assets in the accompanying consolidated balance sheets. The following table provides a reconciliation of cash, cash equivalents, and restricted cash within the consolidated balance sheets that sum to the total of the same such amounts shown in the statements of cash flows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ ​ ​ 2023 2022 2021 ​ ​ ​ (in thousands) ​ Cash and cash equivalents ​ $ 68,802 ​ $ 98,959 ​ $ 117,433 ​ Restricted cash included in deposits and other non-current assets ​ ​ 1,593 ​ ​ 1,515 ​ ​ 1,779 ​ Total cash, cash equivalents, and restricted cash ​ $ 70,395 ​ $ 100,474 ​ $ 119,212 ​ ​ Property and Equipment ​ Property and equipment consists of laboratory equipment, furniture and office equipment, and leasehold improvements and is stated at cost, less accumulated depreciation. Maintenance and repairs that do not improve or extend the lives of the respective assets are expensed to operations as incurred; while costs of major additions and betterments are capitalized. Depreciation is calculated over the estimated useful lives of the assets using the straight-line method. ​ Impairment of Long-Lived Assets ​ The Company evaluates long-lived assets for potential impairment when events or changes in circumstances indicate the carrying value of the assets may not be recoverable. Recoverability is measured by comparing the book values of the assets to the expected future net undiscounted cash flows that the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the book values of the assets exceed their fair value. The Company has not recognized any impairment losses from inception through December 31, 2023. ​ Revenue Recognition ​ The Company enters into license, option, and collaboration agreements which are within the scope of ASC 606, Revenue from Contracts with Customers ​ The promised goods or services in the Company’s arrangements typically consist of license rights to the Company’s intellectual property and research and development services. The Company provides options to additional items in the contracts, which are accounted for as separate contracts when the customer elects to exercise such options, unless the option provides a material right to the customer. The Company evaluates the customer options for material rights, or options to acquire additional goods or services for free or at a discount. If the customer options are determined to represent a material right, the material right is recognized as a separate performance obligation at the outset of the arrangement. Performance obligations are promised goods or services in a contract to transfer a distinct good or service to the customer and are considered distinct when (a) the customer can benefit from the good or service on its own or together with other readily available resources and (b) the promised good or service is separately identifiable from other promises in the contract. In assessing whether promised goods or services are distinct, the Company considers factors such as the stage of development of the underlying intellectual property, the capabilities of the customer to develop the intellectual property on its own or whether the required expertise is readily available and whether the goods or services are integral or dependent to other goods or services in the contract. ​ The Company estimates the transaction price based on the amount expected to be received for transferring the promised goods or services in the contract. The consideration may include fixed consideration or variable consideration. At the inception of each arrangement that includes variable consideration, the Company evaluates the amount of potential payments and the likelihood that the payments will be received. The Company utilizes either the most likely amount method or expected amount method to estimate the amount expected to be received based on which method best predicts the amount expected to be received. The amount of variable consideration which is included in the transaction price may be constrained, and is included in the transaction price only to the extent that it is probable that a significant reversal in the amount of the cumulative revenue recognized will not occur in a future period. ​ The Company’s contracts often include development and regulatory milestone payments which are assessed under the most likely amount method and constrained if it is probable that a significant revenue reversal would occur. Milestone payments that are not within the Company’s control or the licensee’s control, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. At the end of each reporting period, the Company re-evaluates the probability of achievement of such development milestones and any related constraint, and if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect collaboration revenue in the period of adjustment. To date, the Company has not recognized any consideration related to the achievement of development, regulatory, or commercial milestone revenue resulting from any of the Company’s collaboration or license arrangements. ​ For arrangements that include sales-based royalties, including milestone payments based on the level of sales, in which the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (a) when the related sales occur, or (b) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has not recognized any consideration related to sales-based royalty revenue resulting from any of the Company’s collaboration or license arrangements. ​ The Company allocates the transaction price based on the estimated stand-alone selling price of each of the performance obligations. The Company must develop assumptions that require judgment to determine the stand-alone selling price for each performance obligation identified in the contract. The Company utilizes key assumptions to determine the stand-alone selling price for service obligations, which may include other comparable transactions, pricing considered in negotiating the transaction and the estimated costs. Additionally, in determining the standalone selling price for material rights, the Company utilizes comparable transactions, clinical trial success probabilities, and estimates of option exercise likelihood. Variable consideration is allocated specifically to one or more performance obligations in a contract when the terms of the variable consideration relate to the satisfaction of the performance obligation and the resulting amounts allocated are consistent with the amounts the Company would expect to receive for the satisfaction of each performance obligation. ​ The consideration allocated to each performance obligation is recognized as revenue when control is transferred for the related goods or services. For performance obligations which consist of licenses and other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. ​ Upfront payments and fees are recorded as contract liabilities within deferred revenue on the consolidated balance sheets until the Company performs its obligations under these arrangements. Amounts are recorded as accounts receivable when the Company’s right to consideration is unconditional. A portion of revenue recognized from the 2019 and 2023 Neurocrine Collaboration Agreements and the 2023 Novartis Collaboration Agreement is related to performance obligations pursuant to which revenue is recognized using a proportional performance model. Revenue is recognized using input-based measurements, which involves the measurement of progress toward each performance obligation based on the actual costs incurred compared to total projected costs. The Company estimates the expected remaining costs to complete the research and development services for each performance obligation. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure and related revenue recognition. ​ Research and Development ​ Research and development costs are charged to expense as incurred in performing research and development activities. The costs include employee compensation costs, external research, consultant costs, sponsored research, license fees, process development and facilities costs. Facilities costs primarily include the allocation of rent, utilities and depreciation. ​ Leases ​ The Company determines if an arrangement is or contains a lease at inception under Accounting Standards Codification (ASC) 842 Leases ​ Right-of-use assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. Operating lease right-of-use assets and liabilities are recognized at the lease commencement date based on the present value of lease payments over the lease term. As the Company’s leases typically do not provide an implicit rate, the Company uses an estimate of its incremental borrowing rate based on the information available at the lease commencement date in determining the present value of lease payments. Operating lease right-of-use assets also include the effect of any lease prepaid or deferred lease payments and are reduced by lease incentives. The lease terms may include options to extend or terminate the lease when it is reasonably certain that the Company will exercise that option. Lease expense is recognized on a straight-line basis over the lease term. ​ The Company has lease agreements with lease and non-lease components, which are generally accounted for separately. Non-lease components as it pertains to the Company's leased premises generally refer to common area maintenance charges related to the premises. ​ Research Contract Costs and Accruals ​ The Company has entered into various research and development contracts with research institutions and other companies. These agreements are generally cancelable. The Company records accruals for estimated ongoing research costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates may be made in determining the accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates. The Company’s historical accrual estimates have not been materially different from the actual costs. ​ Patent Costs ​ The Company expenses patent application and related legal costs as incurred and classifies such costs as general and administrative expenses in the accompanying statements of operations. ​ Stock-Based Compensation Expense ​ The Company accounts for its stock-based compensation awards in accordance with ASC Topic 718 Compensation—Stock Compensation ​ The Black-Scholes option pricing model requires inputs based on certain subjective assumptions, including (a) the expected stock price volatility, (b) the expected term of the award, (c) the risk-free interest rate and (d) expected dividends. The Company bases the estimate of expected volatility on the historical volatility of its common stock. The historical volatility is calculated based on a period of time commensurate with the expected term assumption. The Company uses the simplified method as prescribed by the SEC Staff Accounting Bulletin No. 107, Share-Based Payment ​ The Company expenses the fair value of its stock-based compensation awards on a straight-line basis over the associated service period, which is generally the period in which the related services are received, adjusted for actual forfeitures of unvested awards as they occur. ​ The Company records the expense for stock-based compensation awards subject to performance conditions over the remaining service period when management determines that achievement of the performance condition is probable. Management evaluates when the achievement of a performance condition is probable based on the expected satisfaction of the performance conditions as of the reporting date. ​ Income Taxes ​ Income taxes are recorded in accordance with ASC Topic 740, Income Taxes reverse. The Company provides a valuation allowance against net deferred tax assets unless, based upon the weight of available evidence, it is more likely than not that the deferred tax assets will be realized. ​ The Company accounts for uncertain tax positions in accordance with the provisions of ASC 740. When uncertain tax positions exist, the Company recognizes the tax benefit of tax positions to the extent that the benefit will more likely than not be realized. The determination as to whether the tax benefit will more likely than not be realized is based upon the technical merits of the tax position as well as consideration of the available facts and circumstances. As of December 31, 2023, the Company does not have any significant uncertain tax positions. ​ Comprehensive Income (Loss) ​ Comprehensive income (loss) is comprised of net income (loss) and other comprehensive income or loss. Other comprehensive income or loss consists of unrealized gains or losses on marketable securities. ​ Net Income (Loss) Per Share ​ Basic net income (loss) per share is calculated by dividing the net income (loss) by the weighted-average number of shares of common stock outstanding during the period, without consideration for potentially dilutive securities. Diluted net income (loss) per share is computed by dividing the net income (loss) by the weighted-average number of shares of common stock and potentially dilutive securities outstanding for the period determined using the treasury-stock and if-converted methods. ​ For purposes of the diluted net income (loss) per share, unvested restricted common stock and outstanding stock options are considered to be potentially dilutive securities. Unvested restricted common stock and outstanding stock options were excluded from the calculation of diluted net loss per share in the years ended December 31, 2023 and 2022, because their effect would be anti-dilutive and therefore, basic and diluted net loss per share were the same for the years ended December 31, 2023 and 2022. ​ The following table sets forth the outstanding potentially dilutive securities that have been excluded in the calculation of diluted net income (loss) per share because to do so would be anti-dilutive: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ ​ ​ 2023 ​ 2022 ​ 2021 ​ Unvested restricted common stock awards ​ 22,500 ​ 45,000 ​ 137,255 ​ Unvested restricted common stock units ​ ​ 1,370,897 ​ ​ 1,112,563 ​ ​ 806,379 ​ Outstanding stock options ​ 7,425,444 ​ 6,199,571 ​ 5,013,193 ​ Total ​ 8,818,841 ​ 7,357,134 ​ 5,956,827 ​ ​ Basic net income (loss) and diluted weighted-average shares outstanding are as follows for the years ended December 31, 2023, 2022, and 2021: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ ​ ​ 2023 ​ 2022 ​ 2021 ​ ​ ​ (in thousands, except share data) ​ Numerator: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net income (loss) ​ $ 132,330 ​ $ (46,408) ​ $ (71,197) ​ Denominator for basic net income (loss) per share: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted average shares outstanding-basic ​ ​ 43,020,747 ​ ​ 38,356,810 ​ ​ 37,668,947 ​ Denominator for diluted net income (loss) per share: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted average shares outstanding ​ ​ 43,020,747 ​ ​ 38,356,810 ​ ​ 37,668,947 ​ Common stock options and restricted stock units ​ ​ 1,548,587 ​ ​ — ​ ​ — ​ Weighted average shares outstanding-diluted ​ ​ 44,569,334 ​ ​ 38,356,810 ​ ​ 37,668,947 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Concentrations of Credit Risk and Significant Suppliers ​ The Company has no financial instruments with off-balance sheet risk such as foreign exchange contracts, option contracts or other foreign currency hedging arrangements. Financial instruments that potentially subject the Company to a concentration of credit risk are cash and cash equivalents. The Company’s cash is held in accounts at financial institutions that may exceed federally insured limits. The Company has not experienced any credit losses in such accounts and does not believe it is exposed to any significant credit risk on these funds. ​ The Company is dependent on third-party manufacturers to supply certain products for research and development activities in its programs. In particular, the Company relies on a sole manufacturer to supply it with specific vectors related to the Company’s research and development programs. ​ Segment Information ​ Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker (“CODM”) in deciding how to allocate resources and assess performance. The Company and the Company’s CODM, the Company’s Chief Executive Officer, view the Company’s operations and manages its business as a single operating segment, which is the business of developing and commercializing genetic medicine. ​ Recent Accounting Pronouncements ​ In August 2020, the Financial Accounting Standards Board (“FASB”) issued ASU No. 2020-06, Debt – Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging—Contracts in Entity’s Own Equity (Subtopic 815-40) ​ In November 2023 the FASB issued ASU No. 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosure ​ In December 2023, the FASB issued ASU 2023-09, “ Income Taxes (Topic 740) - Improvements to Income Tax Disclosures.”

Fair value measurements

Fair value measurements	12 Months Ended
	Dec. 31, 2023
Fair value measurements
Fair value measurements	3. Fair value measurements ​ Assets and liabilities measured at fair value on a recurring basis as of December 31, 2023 and 2022 are as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Quoted Prices ​ Significant ​ ​ ​ ​ ​ ​ ​ ​ in Active ​ Other ​ Significant ​ ​ ​ ​ ​ Markets for ​ Observable ​ Unobservable ​ ​ ​ ​ ​ Identical Assets ​ Inputs ​ Inputs ​ Assets Total (Level 1) (Level 2) (Level 3) ​ ​ (in thousands) December 31, 2023 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds included in cash and cash equivalents ​ $ 65,589 ​ $ 65,589 ​ $ — ​ $ — ​ Marketable securities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ U.S. Treasury notes ​ ​ 103,044 ​ ​ 103,044 ​ ​ — ​ ​ — ​ U.S. Government agency securities ​ ​ 31,075 ​ ​ 31,075 ​ ​ — ​ ​ — ​ Corporate bonds ​ ​ 23,970 ​ ​ — ​ ​ 23,970 ​ ​ — ​ Commercial paper ​ ​ 3,985 ​ ​ — ​ ​ 3,985 ​ ​ — ​ Total money market funds and marketable securities ​ $ 227,663 ​ $ 199,708 ​ $ 27,955 ​ $ — ​ December 31, 2022 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds included in cash and cash equivalents $ 91,724 ​ $ 91,724 ​ $ — $ — ​ Marketable securities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ U.S. Treasury notes ​ 19,889 ​ ​ 19,889 ​ ​ — ​ ​ — ​ Total money market funds and marketable securities $ 111,613 ​ $ 111,613 ​ $ — ​ $ — ​ ​ The Company measures the fair value of money market funds, U.S. Treasury notes and U.S. Government agency securities based on quoted prices in active markets for identical securities. The Company measures the fair value of the Level 2 securities, corporate bonds and commercial paper, based on recent trades of securities in inactive markets or based on quoted market prices of similar instruments and other significant inputs derived from or corroborated by observable market data.

Prepaid expenses and other curr

Prepaid expenses and other current assets	12 Months Ended
	Dec. 31, 2023
Prepaid expense and other current assets
Prepaid expenses and other current assets	4. Prepaid expenses and other current assets ​ Prepaid expenses and other current assets consist of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ 2023 2022 ​ ​ (in thousands) ​ Other current assets ​ $ 2,628 ​ $ 4,233 ​ Prepaid insurance ​ 607 ​ 696 ​ Prepaid research and development contracts 1,119 ​ ​ 83 ​ Accrued interest receivable ​ ​ 964 ​ ​ 382 ​ Total ​ $ 5,318 ​ $ 5,394 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Property and equipment, net

Property and equipment, net	12 Months Ended
	Dec. 31, 2023
Property and equipment, net
Property and equipment, net	5. Property and equipment, net ​ Property and equipment, net consists of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ ​ 2023 2022 ​ ​ (in thousands) ​ Laboratory equipment ​ $ 20,536 ​ $ 19,675 ​ Leasehold improvements ​ ​ 7,106 ​ ​ 12,554 ​ Furniture and office equipment ​ 2,625 ​ 2,333 ​ Other ​ ​ 1,265 ​ 502 ​ Total property and equipment ​ 31,532 ​ 35,064 ​ Less: accumulated depreciation ​ (15,038) ​ (17,207) ​ Property and equipment, net ​ $ 16,494 ​ $ 17,857 ​ ​ The Company recorded $4.4 million, $6.2 million, and $5.2 million in depreciation expense during the years ended December 31, 2023, 2022, and 2021, respectively.

Accrued expenses

Accrued expenses	12 Months Ended
	Dec. 31, 2023
Accrued expenses
Accrued expenses	6. Accrued expenses ​ Accrued expenses consist of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ ​ 2023 2022 ​ ​ (in thousands) ​ Employee compensation costs ​ $ 6,614 ​ $ 4,559 ​ Research and development costs ​ ​ 5,225 ​ ​ 1,895 ​ Accrued goods and services ​ 4,229 ​ 636 ​ Professional services ​ 755 ​ 726 ​ Total ​ $ 16,823 ​ $ 7,816 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Lease obligation

Lease obligation	12 Months Ended
	Dec. 31, 2023
Lease obligation
Lease obligation	7. Lease obligation ​ Operating Leases ​ As of December 31, 2023, the Company has a lease for laboratory and office space at 75 Hayden Avenue in Lexington, Massachusetts through January 31, 2031 and a lease for additional office and laboratory space at 64 Sidney Street in Cambridge, Massachusetts through November 30, 2026. ​ In September 2021, the Company entered into an agreement with BioNTech US, Inc. (“BioNTech US”) to sublease part of the office and laboratory space leased by the Company at 75 Sidney Street in Cambridge, Massachusetts (the “Sublease Agreement”) at that time. The sublease term was for approximately 3.3 years. The sublease did not relieve the Company of its original obligation under the lease, and therefore the Company did not adjust the operating lease right-of-use asset as a result of the sublease and accounted for the sublease as a separate lease. ​ On June 22, 2022 the Company entered into a Lease Termination Agreement (the “Lease Termination Agreement”) and terminated the lease for office and laboratory space at 75 Sidney Street (the “75 Sidney Street Lease”), effective immediately. In connection with the Lease Termination Agreement, the Company also entered into a Sublease Termination Agreement (the “Sublease Termination Agreement”) and terminated the Sublease Agreement with BioNTech US. The Company did not incur any termination penalties in connection with the Lease Termination Agreement or Sublease Termination Agreement. The Company derecognized the related right-of-use asset of approximately $14.5 million and the operating lease liabilities of $17.0 million, accordingly, resulting in a gain of $2.5 million in the year ended December 31, 2022. ​ The Company’s lease agreements require the Company to maintain a cash deposit or irrevocable letter of credit in the aggregate amount of $1.5 million payable to its landlords as security for the performance of its obligations under the leases. ​ On August 11, 2023, the Company entered into a first amendment (the “First Amendment”) to its existing lease for laboratory and office space at 75 Hayden Avenue in Lexington, Massachusetts, pursuant to which the Company agreed to lease approximately 61,307 square feet of additional office and laboratory space. The term of the First Amendment commences on the date on which the landlord makes the space available for use by the Company, and expires on January 31, 2031, unless sooner terminated or extended. As of December 31, 2023, the Company did not have control of the space and therefore, the lease had not yet commenced. The commencement date for the First Amendment occurred on February 1, 2024. The expected contractual obligation under the First Amendment to the Company’s existing lease is approximately $37.8 million, to be paid over the 7 year term of the lease. ​ Total lease cost for operating leases of approximately $3.6 million, $4.6 million, and $6.8 million was incurred during the years ended December 31, 2023, 2022, and 2021, respectively. As of December 31, 2023, the weighted average remaining lease term was 5 years and the weighted average incremental borrowing rate used to determine the operating lease liability was 7.4%. ​ The following table summarizes the operating sublease income generated under the Sublease Agreement for the years ended December 31, 2023, 2022, and 2021: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Years ended ​ December 31, ​ 2023 2022 ​ 2021 ​ (in thousands) Operating sublease income $ — ​ $ 1,380 ​ $ 838 ​

Commitments, contingencies, and

Commitments, contingencies, and other liabilities	12 Months Ended
	Dec. 31, 2023
Commitments, contingencies, and other liabilities
Commitments, contingencies, and other liabilities	8. Commitments, contingencies, and other liabilities ​ As of December 31, 2023 and 2022, other current and non-current liabilities consisted of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ ​ 2023 2022 ​ ​ (in thousands) ​ Other current liabilities ​ ​ ​ ​ ​ ​ Lease liabilities ​ 3,200 ​ ​ 2,832 ​ Total other current liabilities $ 3,200 ​ $ 2,832 ​ ​ ​ ​ ​ ​ ​ ​ Other non-current liabilities ​ ​ ​ ​ ​ ​ Lease liabilities $ 17,093 ​ $ 20,294 ​ Other ​ 1,001 ​ ​ 1,001 ​ Total other non-current liabilities $ 18,094 ​ $ 21,295 ​ ​ Strategic Restructuring ​ On August 6, 2021, the board of directors of the Company approved a strategic restructuring plan to eliminate a portion of its workforce as part of an initiative to reduce expenses and enhance operations. The strategic restructuring plan was approved in connection with its portfolio reevaluation efforts and its strategic shift to invest additional resources in the Company’s TRACER Capsid development efforts. ​ During the year ended December 31, 2021, the Company incurred restructuring costs of approximately $2.6 million, which consists of severance-related costs. These costs are reported within the Company’s research and development expenses and general and administrative expenses. All costs have been paid as of December 31, 2023. ​ Litigation ​ The Company was not a party to any material legal matters or claims and did not have contingency reserves established for any litigation liabilities as of December 31, 2023 or 2022.

Significant Agreements

Significant Agreements	12 Months Ended
	Dec. 31, 2023
Significant Agreements
Significant Agreements	9. Significant Agreements 2023 Novartis License and Collaboration Agreement ​ On December 28, 2023 (the “2023 Novartis Collaboration Agreement Effective Date”), the Company entered into a License and Collaboration Agreement (the “2023 Novartis Collaboration Agreement”) with Novartis to (a) provide rights to Novartis with respect to certain TRACER Capsids for use in the research, development, and commercialization by Novartis of AAV gene therapy products and product candidates, comprising such TRACER Capsids and payloads intended for the treatment of spinal muscular atrophy (the “Novartis SMA Program”) and (b) collaborate to develop AAV gene therapy products and product candidates intended for the treatment of Huntington’s disease (the “Novartis HD Program”), in each case, leveraging TRACER Capsids and other intellectual property controlled by the Company. ​ Novartis SMA Program and Novartis HD Program Licenses ​ Under the terms of the 2023 Novartis Collaboration Agreement, the Company granted Novartis and its affiliates: ​ ● a non-exclusive, non-transferable, non-sublicensable (except in limited circumstances for contractors), worldwide, royalty-free right and license under any patents or know-how controlled by the Company and related to the TRACER Capsids to evaluate the same for use in the development of a product or product candidate under the Novartis SMA Program (a “Novartis SMA Program Product”) comprising such a TRACER Capsid and a payload selected by Novartis during the period beginning on the 2023 Novartis Collaboration Agreement Effective Date and ending on the third anniversary of the 2023 Novartis Collaboration Agreement Effective Date; ● an exclusive (even as to the Company), sublicensable, non-transferable, worldwide, royalty-bearing right and license under any patents or know-how controlled by the Company and relating to the selected TRACER Capsids to exploit the same as incorporated into a Novartis SMA Program Product for all human and veterinary diagnostic, prophylactic and therapeutic uses during the Term (as defined below); and ● an exclusive (even as to the Company), non-transferable, sublicensable, worldwide, royalty-bearing right and license under any patents and know-how controlled by the Company and relating to the development of a product or product candidate under the Novartis HD Program (a “Novartis HD Program Product”) to exploit the same for all human and veterinary diagnostic, prophylactic and therapeutic uses during the Term. Governance ​ The Company and Novartis have agreed to manage the Novartis HD Program through a joint steering committee until dissolved after the first IND application filing for a Novartis HD Program Product. The Company and Novartis have further agreed that day-to-day activities of both the Novartis SMA Program and the Novartis HD Program shall be managed through designees from each of the Company and Novartis, acting as alliance managers. ​ Development, Regulatory Approval, Commercialization and Diligence ​ Under the 2023 Novartis Collaboration Agreement, Novartis is solely responsible for, and has sole decision-making authority with respect to, at its own expense, the exploitation of a Novartis SMA Program Product. ​ With respect to the Novartis HD Program, the parties have agreed to conduct research and pre-clinical development of Novartis HD Program Products pursuant to a research plan, with Novartis reimbursing the Company for its activities thereunder in accordance with the agreed-to budget. From and after the first IND application filing for the Novartis HD Program, the parties have agreed that Novartis will assume sole responsibility for the development and commercialization of Novartis HD Program Products, including all further preclinical and clinical development and any commercialization of the Novartis HD Program products and product candidates. ​ With respect to each of the Novartis SMA Program Products and Novartis HD Program Products, Novartis is obligated to use commercially reasonable efforts to develop and obtain regulatory approval for at least one of each such product in the United States and in certain other international markets specified in the 2023 Novartis Collaboration Agreement. ​ Termination ​ Unless earlier terminated, with respect to any licensed product(s) under the Collaboration Agreement, on a country-by-country basis, the 2023 Novartis Collaboration Agreement expires upon the expiration of the last-to-expire royalty term with respect to such licensed product in such country in the territory. Subject to a cure period, either party may terminate the 2023 Novartis Collaboration Agreement, in whole or in part, subject to specified conditions, in the event of the other party’s uncured material breach. Novartis may also terminate the 2023 Novartis Collaboration Agreement, in whole or in part, subject to specified conditions, for the Company’s insolvency, for the occurrence of a violation of global trade control laws, or for the Company’s non-compliance with certain anti-bribery or anti-corruption covenants. Novartis may terminate the 2023 Novartis Collaboration Agreement, in whole or in part, for any or no reason upon ninety days’ written notice to the Company. In the event that Novartis has the right to terminate the 2023 Novartis Collaboration Agreement as a result of an uncured material breach by the Company that materially impairs the ability of Novartis to exploit one or more licensed products, Novartis may, in lieu of such termination, elect for the 2023 Novartis Collaboration Agreement to remain in full force and effect, and all milestone payments and royalties that would have otherwise been payable by Novartis under such licenses had the 2023 Novartis Collaboration Agreement not been breached would be substantially reduced. ​ Financial Terms ​ Under the 2023 Novartis Collaboration Agreement, Novartis agreed to pay the Company an initial upfront payment of $80.0 million. The Company is eligible to receive specified development, regulatory, and commercialization milestone payments of up to an aggregate of $200.0 million for the Novartis SMA Program and up to an aggregate of $225.0 million for the Novartis HD Program, in each case for the first corresponding product to achieve the corresponding milestone. The Company is also eligible to receive (a) specified sales milestone payments of up to an aggregate of $400.0 million for the Novartis SMA Program and up to an aggregate of $375.0 million for the Novartis HD Program and (b) tiered, escalating royalties in the high single-digit to low double-digit percentages of annual net sales of the Novartis SMA Program Products and the Novartis HD Program Products. The royalties are subject to potential customary reductions, including patent claim expiration, payments for certain third-party licenses, and biosimilar market penetration, subject to specified limits. ​ Stock Purchase Agreement ​ Under the stock purchase agreement with Novartis entered into on December 28, 2023 (the “2023 Novartis Stock Purchase Agreement”), Novartis agreed to purchase 2,145,002 shares of common stock of the Company (the “Novartis Shares”) for an aggregate purchase price of approximately $20.0 million. ​ Accounting Analysis ​ The Company determined the 2023 Novartis Collaboration Agreement represents a contract with a customer under ASC 606. In addition, the 2023 Novartis Collaboration Agreement did not modify the scope or price of the 2022 Novartis Option and License Agreement, as discussed below. The Company therefore determined that the 2023 Novartis Collaboration Agreement should be accounted for separately. The 2023 Novartis Collaboration Agreement includes the following performance obligations: (i) the development and commercialization license for the Novartis SMA Program, (ii) the development and commercialization license for the Novartis HD Program; and (iii) the research and development services for the Novartis HD Program (“Novartis HD Research Services”). The development and commercialization licenses for the Novartis HD Program and Novartis SMA Program are each distinct, as Novartis can benefit from such licenses on their own or from other resources commonly available in the industry given the stage of development of the product candidates subject to the licenses. Similarly, the research and development services for the Novartis HD Program provide a distinct benefit to Novartis within the context of the contract, separate from the licenses. ​ The transaction consideration allocated to the performance obligations within the 2023 Novartis Collaboration Agreement includes fixed consideration of $80.0 million, and variable consideration, which is comprised of an estimated $24.2 million of cost reimbursements for Novartis HD Research Services, up to $425.0 of potential development milestone payments, up to $775.0 million of potential sales milestone payment, and sales-based royalties. The consideration related to the Novartis HD Research Services, becomes due and payable on a quarterly basis as the services are being performed. ​ The Company estimates variable consideration using the most likely amount approach. At the outset of the contract, the Company has determined this consideration should be constrained. The sales milestone payments and royalties will be recognized in the period the underlying sales occur, as this consideration is related to the two development and commercialization licenses, the predominant performance obligations in the contract. ​ The Company allocated the fixed transaction price to the separate performance obligations based on the relative standalone selling price of each performance obligation. The standalone selling prices for development and commercialization licenses for the Novartis SMA Program and Novartis HD Program were estimated using an adjusted-market approach. The Company allocated the variable consideration related to the Novartis HD Research Services as the consideration becomes payable as the Company delivers the Novartis HD Research Services and allocating the entirety of this consideration to the Novartis HD Research Services reflects the amount the Company expects to be entitled to for performing the services. The development milestone payments, the sales milestone payments and the royalties are allocated to the respective development and commercialization licenses for the Novartis SMA Program and Novartis HD Program as the variable consideration relates directly to those performance obligations. ​ The Company recognized the $80.0 million fixed transaction price allocated to the development and commercialization licenses for the Novartis SMA Program and Novartis HD Program, as collaboration revenue upon delivery of the development and commercialization licenses to Novartis in December 2023. The issuance of the Novartis Shares to Novartis pursuant to the 2023 Novartis Stock Purchase Agreement in January 2024 resulted in a premium of $0.7 million. The premium will be allocated to the development and commercialization licenses for the Novartis HD Program and Novartis SMA Program and is expected to be recognized as collaboration revenue during the first quarter of 2024, upon the issuance of the Novartis Shares under the 2023 Novartis Stock Purchase Agreement. The Novartis HD Research Services commenced in the first quarter of 2024. The $80.0 million fixed transaction price was recorded in accounts receivable as of December 31, 2023. The Company had an unconditional right to the payment, and it was collected in January of 2024. ​ The Company incurred approximately $1.9 million of business development costs related to the 2023 Novartis Collaboration Agreement which were payable only upon the execution of the agreement, and therefore are considered incremental costs of obtaining a contract with a customer. Given the substantial value associated with the development and commercialization licenses for the Novartis SMA Program and Novartis HD Program that were delivered in December 2023, the Company recognized the $1.9 million of costs in general and administrative expenses during the year ended December 31, 2023. ​ 2022 Novartis Option and License Agreement ​ Summary of Agreement ​ On March 4, 2022 (the “Novartis Effective Date”), the Company entered into an option and license agreement with Novartis (the “2022 Novartis Agreement”). Pursuant to the 2022 Novartis Agreement, the Company granted Novartis options (the “Novartis License Options”) to license TRACER Capsids (“Novartis Licensed Capsids”) for exclusive use with certain targets to develop and commercialize adeno-associated virus gene therapy candidates comprised of Novartis Licensed Capsids and payloads directed to such targets (the “Novartis Payloads”). ​ During the period commencing on the Novartis Effective Date and ending on the first anniversary thereof or, in the event Novartis exercises a Novartis License Option, the third anniversary thereof, on a target-by-target basis (the “Novartis Research Term”), the Company granted Novartis a non-exclusive research license to evaluate the Company’s TRACER Capsids for potential use, in combination with Novartis Payloads, in programs targeting three specified genes (the “Initial Novartis Targets”). Upon the payment of additional fees, Novartis may also assess the Company’s TRACER Capsids for use with up to two other targets (the “Additional Novartis Targets”), subject to certain conditions including that such target is not part of, or reasonably competitive with, the Company’s current development programs (the Initial Novartis Targets and the Additional Novartis Targets collectively, the “Novartis Targets”). During the Novartis Research Term, as applicable, the Company may, at its sole discretion and expense, conduct further research activities to identify additional TRACER Capsids. If the Company elects to do so, the Company has agreed to disclose performance characteristics of such new TRACER Capsids to Novartis on a rolling basis. ​ During the applicable Novartis Research Term, Novartis may exercise up to three Novartis License Options—or up to five Novartis License Options if Novartis is evaluating the Additional Novartis Targets—in the aggregate, provided that Novartis may only exercise one Novartis License Option for each Novartis Target. Upon the exercise of any Novartis License Option, the Company has agreed to grant Novartis a target-exclusive, worldwide license, with the right to sublicense, under certain of the Company’s intellectual property, the rights to develop and commercialize the applicable Novartis Licensed Capsid as incorporated into products containing the corresponding Novartis Payload (the “Novartis Licensed Products”). Upon the exercise of a Novartis License Option, the Company has agreed to provide certain additional know-how to enable Novartis to exploit the Novartis Licensed Capsid and the corresponding Novartis Payload for use in a Novartis Licensed Product. Novartis may, during the applicable Novartis Research Term but following the exercise of a Novartis License Option, conduct additional evaluation of the Company’s capsid candidates and has the right to substitute any other TRACER Capsid for a Novartis Licensed Capsid. ​ Effective March 1, 2023, Novartis exercised its Novartis License Options to license TRACER Capsids for use in gene therapy programs against two undisclosed Initial Novartis Targets. ​ Subject to the Company’s disclosure obligations described above, the Company and Novartis have agreed to conduct their respective research and evaluation activities independently, with communications being managed by two alliance managers comprised of a designee from each of the Company and Novartis. ​ Under the 2022 Novartis Agreement, Novartis is solely responsible for, and has sole decision-making authority with respect to, development and commercialization of the Novartis Licensed Products. In the event Novartis exercises a Novartis License Option, Novartis is required to use commercially reasonable efforts to develop and obtain regulatory approval for at least one Novartis Licensed Product for each Novartis Target for which it has exercised a Novartis License Option in (a) the United States and (b) at least three of the following countries: the United Kingdom, France, Germany, Italy, Spain and Japan (each of which, a “Novartis Major Market Country”), subject to certain limitations. Novartis is also required to use commercially reasonable efforts to commercialize each Novartis Licensed Product in the United States and at least three Novartis Major Market Countries where Novartis or its designated affiliates or sublicensees has received regulatory approval for such Novartis Licensed Product, subject to certain limitations. ​ During the Novartis Research Term, the Company has agreed to provide plasmids to Novartis for the production of TRACER Capsids for evaluation upon request. The Company has also granted Novartis a non-exclusive license, effective upon an exercise of a Novartis License Option and in addition to its options for target-exclusive licenses under certain of the Company’s intellectual property described above, on a Novartis Licensed Capsid-by-Novartis Licensed Capsid basis, under certain of the Company’s know-how to exploit the applicable Novartis Licensed Capsid as incorporated into Novartis Licensed Products containing the corresponding Novartis Payload. ​ Under the terms of the 2022 Novartis Agreement, Novartis paid the Company an upfront payment of $54.0 million. Effective as of March 1, 2023, Novartis exercised its Novartis License Options to license TRACER Capsids for use in gene therapy programs against two undisclosed Initial Novartis Targets. ​ Under the terms of the 2022 Novartis Agreement, each party owns the entire right, title, and interest in and to all patents or know-how controlled by such party and existing as of or before the Novartis Effective Date, or invented, developed, created, generated or acquired solely by or on behalf of such party after the Novartis Effective Date. Subject to certain specified exceptions, any patents and know-how that are invented or otherwise developed jointly by or on behalf of the parties during the term of the 2022 Novartis Agreement and in the course of the parties’ activities under the 2022 Novartis Agreement will follow inventorship under U.S. patent law. ​ Subject to certain limitations and exceptions, the Company has agreed (a) during the Novartis Research Term, not to conduct any internal program or program on behalf of a third party that is directed to the development or commercialization of any Company’s capsids, or grant any third party or affiliate any right or license under the Company’s rights in such capsids, to exploit any therapeutic product containing a capsid in combination with a payload designed to have therapeutic effect on any of the Novartis Targets; and (b) after Novartis’s exercise of any Novartis License Option, not to grant any third party or affiliate any right or license under the Company’s patents to exploit any Novartis Licensed Capsid for the applicable Novartis Target. ​ Unless earlier terminated, the 2022 Novartis Agreement expires on the expiration of the last-to-expire royalty term with respect to all Novartis Licensed Products in all countries. Subject to a cure period, either party may terminate the 2022 Novartis Agreement, in whole or in part, subject to specified conditions, in the event of the other party’s uncured material breach. Novartis may also terminate the 2022 Novartis Agreement, in whole or in part, subject to specified conditions, for the Company’s insolvency, the occurrence of a violation of global trade control laws, or for the Company’s non-compliance with certain anti-bribery or anti-corruption covenants. Novartis may terminate the 2022 Novartis Agreement, in whole or in part, for any or no reason upon ninety days’ written notice to the Company. ​ Upon certain terminations for cause by Novartis, the licenses granted by the Company to Novartis under the 2022 Novartis Agreement shall become irrevocable and perpetual, and all milestone payments and royalties that would have otherwise been payable by Novartis under such licenses had the Novartis Agreement remained in effect would be substantially reduced. ​ Accounting Analysis ​ At inception, the Company determined the 2022 Novartis Agreement was a contract with a customer under ASC 606. The Company assessed the promised goods and services and determined that the 2022 Novartis Agreement contains three performance obligations consisting of three material rights, one for each of the Novartis License Options. The Company concluded that each Novartis License Option provides a material right as consideration for each option is less than the amount that the Company would otherwise have expected to receive outside the context of the contract. The promises at inception do not include the underlying goods or services that would be delivered upon exercise of the option, but rather represent the value to the customer of having the right to exercise the Novartis License Option at the specified exercise fee. Upon the exercise of a Novartis License Option, until March 4, 2025, while the Company is not obligated to conduct additional research activities upon any option exercise to identify additional proprietary capsids that may be useful for AAV gene therapies for the treatment of central nervous system or cardiovascular diseases, it has agreed to continue to disclose to Novartis, on a rolling basis, the performance characteristics identified for all such capsid candidates, if and when available. Novartis may conduct additional evaluation of such capsid candidates and has the right to substitute any other capsid candidate for the Novartis Licensed Capsid it previously elected to license when it exercised the Novartis License Option. The Company determined that this promise to provide Novartis the ability to evaluate and potentially substitute other capsid candidates for the Novartis Licensed Capsid it previously elected to license when it exercised the Novartis License Option, if and when available, is an additional performance obligation in the arrangement (the “Novartis Substitution Right Performance Obligation”). The Company concluded the options for Additional Novartis Targets are not material rights as the price reflects the standalone selling price of the options. The Company will therefore account for the options for Additional Novartis Targets separately, if and when exercised. ​ The Company received a nonrefundable, upfront payment of $54.0 million as consideration under the 2022 Novartis Agreement, which represents the transaction price at inception. Additional consideration to be paid to the Company upon exercise of the Novartis License Options or upon reaching certain milestones are excluded from the transaction price as they relate to option fees and milestones that could only be achieved subsequent to an option exercise. ​ The Company allocated the transaction price to the three material rights based on their relative standalone selling prices. The estimated standalone selling price for each material right was based on an adjusted market assessment approach. The Company concluded that the market would be willing to pay an equal amount for each Novartis License Option on a standalone basis. The Company reached this conclusion after considering (i) the downstream economics including option fees, milestones and royalties related to each Novartis License Option being identical and (ii) comparable market data. The Company determined the standalone selling price for the Novartis Substitution Right Performance Obligation was insignificant to the allocation of the transaction price using the relative standalone selling price model and did not allocate any transaction price to the Novartis Substitution Right Performance Obligation, accordingly. This determination was supported by qualitative and quantitative assessments of the standalone selling price that considered the cost of identifying other potential capsid candidates and the likelihood of license substitution. As such, based on the relative standalone selling price for each of the three material rights, the allocation of the transaction price to the separate performance obligations is $18.0 million for each material right. ​ The amount allocated to each material right was recorded as deferred revenue. ​ During the year ended December 31, 2023, the Company recognized $79.0 million in collaboration revenue related to the Novartis Agreement. Of this $79.0 million, $54.0 million is attributable to the exercise of the two material rights for Novartis License Options and the expiration of the third material right and was previously deferred as of December 31, 2022. The remaining $25.0 million represents the option exercise fee. This amount was received by the Company during the second quarter of 2023. ​ 2023 Neurocrine Collaboration Agreement ​ Summary of Agreement ​ On January 8, 2023, the Company entered into a collaboration and license agreement with Neurocrine (the “2023 Neurocrine Collaboration Agreement”) for the research, development, manufacture and commercialization of gene therapy products directed to the GBA1 Program, and three early research programs focused on the research, development, manufacture and commercialization of gene therapies designed to address central nervous system (“CNS”) diseases or conditions associated with rare genetic targets (the “2023 Discovery Programs” and, collectively with the GBA1 Program, the “2023 Neurocrine Programs”). The 2023 Neurocrine Collaboration Agreement became effective on February 21, 2023 (the “Neurocrine Effective Date”). ​ Collaboration and License ​ Under the 2023 Neurocrine Collaboration Agreement, the Company and Neurocrine have agreed to collaborate on the conduct of the 2023 Neurocrine Programs. Under the terms of the 2023 Neurocrine Collaboration Agreement, subject to the rights retained by the Company thereunder, the Company granted to Neurocrine, as of the Neurocrine Effective Date, an exclusive, royalty-bearing, sublicensable, worldwide license, under certain of the Company’s intellectual property rights, to research, develop, manufacture and commercialize gene therapy products (the “2023 Collaboration Products”), arising under the 2023 Neurocrine Programs. ​ Pursuant to mutually-agreed development plans, during the period beginning on the Neurocrine Effective Date and ending on the third anniversary of the Neurocrine Effective Date, which period may be extended upon mutual written agreement of the Company and Neurocrine (the “2023 Discovery Period”), and as overseen by the Joint Steering Committee (“JSC”) for the ongoing collaboration with Neurocrine, the Company is responsible for identifying capsids meeting target criteria, producing development candidates, and conducting other pre-clinical activities regarding the 2023 Collaboration Products. Neurocrine has agreed to be responsible for all costs the Company incurs in conducting pre-clinical development activities for each 2023 Neurocrine Program, in accordance with JSC agreed upon workplans and budgets. If the Company breaches its responsibilities during this time or, in certain circumstances, upon a change of control, Neurocrine has the right, but not the obligation, to assume the conduct of the Company’s activities under such 2023 Neurocrine Program. ​ The Company has been granted the option (“2023 Co-Co Option”) to co-develop and co-commercialize 2023 Collaboration Products in the GBA1 Program in the United States upon the occurrence of the Company receiving topline data from the first Phase 1 clinical trial for a product candidate being developed pursuant to the GBA1 Program. Should the Company elect to exercise its 2023 Co-Co Option, the Company and Neurocrine agree to enter into a cost and profit-sharing arrangement (a “2023 Co-Co Agreement”), whereby the Company and Neurocrine agree to jointly develop and commercialize 2023 Collaboration Products in the GBA1 Program (“2023 Co-Co Products”) in the United States and share equally in the GBA1 Program’s costs, profits and losses in the United States, with each party entitled to or responsible for 50% of profits and losses with respect to each 2023 Co-Co Product in the United States, subject to specified exceptions. The parties have agreed that the 2023 Co-Co Agreement will provide the Company the right to terminate the 2023 Co-Co Agreement for any reason upon prior written notice to Neurocrine and provide Neurocrine the right to terminate or amend the 2023 Co-Co Agreement upon a change of control under certain circumstances. In the event the Company exercises its 2023 Co-Co Option, the parties have also agreed that Neurocrine is entitled to receive (in addition to its 50% share of profits) 50% of the Company’s share of profits until the Company’s obligation to repay 50% of all development costs incurred by Neurocrine in connection with the GBA1 Program prior to such exercise have been paid off out of such 50% of the Company’s share of profits. ​ Candidate Selection ​ Either party may notify the JSC of any gene therapy product candidate that includes a Company capsid and a payload that is being developed under a 2023 Neurocrine Program (a “Collaboration Candidate”), that it desires to nominate as a development candidate. In such event, the JSC shall determine whether such nominated Collaboration Candidate meets certain development criteria. There will be a maximum of four potential development candidates for which development is being performed under any 2023 Neurocrine Program at any given time during the 2023 Discovery Period. If a Collaboration Candidate fails to meet criteria established by the JSC and is removed from consideration to become a development candidate or is named a development candidate, then a new Collaboration Candidate may be nominated to be a potential development candidate to replace the Collaboration Candidate that has failed or succeeded such that not more than four potential development candidates per program are under consideration at any one time during the 2023 Discovery Period. ​ Manufacturing ​ The parties have agreed that the applicable development plans shall specify the allocation between the Company and Neurocrine of responsibilities for the manufacturing of Collaboration Candidates associated with the applicable 2023 Neurocrine Program during the 2023 Discovery Period. In accordance with the 2023 Collaboration Agreement, the parties have also agreed that, if the Company conducts any portion of the manufacturing of a Collaboration Candidate, the applicable development plan shall include an obligation for the Company to assist with the technology transfer of such manufacturing responsibilities to Neurocrine or a third-party contract manufacturing organization, as reasonably requested by Neurocrine, on terms to be mutually-agreed by the Company and Neurocrine. Following the end of the 2023 Discovery Period, Neurocrine shall be responsible for the manufacturing of all Collaboration Candidates and products. ​ Financial Terms ​ Under the terms of the 2023 Neurocrine Collaboration Agreement, Neurocrine paid the Company an upfront payment of approximately $136.0 million and approximately $39.0 million for the purchase of 4,395,588 shares of common stock of the Company at a price of $8.88 per share in February 2023. The 2023 Collaboration Agreement provides for aggregate development milestone payments from Neurocrine to the Company for 2023 Collaboration Products under (a) the GBA1 Program of up to $985.0 million; and (b) each of the three 2023 Discovery Programs of up to $175.0 million for each 2023 Discovery Program. The Company may be entitled to receive aggregate commercial milestone payments for up to two 2023 Collaboration Products under the GBA1 Program of up to $950.0 million per 2023 Collaboration Product and for one 2023 Collaboration Product under each 2023 Discovery Program of up to $275.0 million per 2023 Discovery Program. ​ Neurocrine has also agreed to pay the Company tiered royalties, based on future net sales of the 2023 Collaboration Products. Such royalty percentages, for net sales in and outside the United States, range from (a) for the GBA1 Program, the low double-digits to twenty and the high single-digits to mid-teens, respectively, and (b) for each 2023 Discovery Program, high single-digits to mid-teens and mid-single digits to low double-digits, respectively. On a country-by-country and 2023 Neurocrine Program-by-2023 Neurocrin

Common stock

Common stock	12 Months Ended
	Dec. 31, 2023
Common stock.
Common stock	10. Common stock ​ As of December 31, 2023 and 2022, the Company had authorized 120,000,000 shares of common stock, at $0.001 par value per share. ​ General ​ The voting, dividend and liquidation rights of the holders of the common stock are subject to and qualified by the rights, powers and preferences of the holders of preferred stock. The common stock has the following characteristics: ​ Liquidation ​ The holders of shares of common stock are entitled to share ratably in the Company’s remaining assets available for distribution to its stockholders in the event of any voluntary or involuntary liquidation, dissolution or winding up of the Company or upon occurrence of a deemed liquidation event. ​ Shares Reserved For Future Issuance ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ ​ 2023 2022 Shares reserved for vesting of restricted stock awards under the Founder Agreements 22,500 ​ 45,000 ​ Shares reserved for exercise of outstanding stock options 7,425,444 ​ 6,199,571 Shares reserved for vesting of outstanding restricted stock units 1,370,897 ​ 1,112,563 Shares reserved for issuances under the 2015 Stock Option Plan ​ 3,572,195 ​ 3,536,932 ​ Shares reserved for issuances under the 2015 Employee Stock Purchase Plan ​ 2,158,966 ​ 1,884,309 ​ ​ 14,550,002 ​ 12,778,375 ​

Stock-based compensation

Stock-based compensation	12 Months Ended
	Dec. 31, 2023
Stock-based compensation
Stock-based compensation	11. Stock-based compensation ​ 2014 Stock Option and Grant Plan ​ In January 2014, the Company adopted the 2014 Stock Option and Grant Plan (the “2014 Plan”), under which it could grant incentive stock options, non-qualified stock options, restricted stock awards, unrestricted stock awards, or restricted stock units to purchase up to 823,529 shares of common stock to employees, officers, directors and consultants of the Company. ​ The terms of stock option agreements, including vesting requirements, were determined by the board of directors and were subject to the provisions of the 2014 Plan. Restricted stock awards granted by the Company generally vest based on each grantee’s continued service with the Company during a specified period following grant. Stock options granted to employees generally vest over four years, with 25% vesting on the one year anniversary and 75% vesting ratably, on a monthly basis, over the remaining three years. Stock options granted to non-employee consultants generally vest monthly over a period of one ​ Founder Awards ​ In January 2014, the Company issued 1,188,233 shares of restricted stock to its founders (each, a “Founder”) at an original issuance price of $0.0425 per share. Of the total restricted shares awarded to the Founders, 835,292 shares were slated to vest over one ​ The remainder of the restricted stock awards were slated to vest upon the achievement of certain performance objectives as well as continued service to the Company, as set forth in the agreements. Stock-based compensation expense associated with these performance-based awards is recognized when the achievement of the performance condition is considered probable, using management’s best estimates. The Company has modified certain of the awards, including repurchasing a total of 131,470 shares underlying the awards through December 31, 2023, and modifying the vesting provisions such that the modified awards vest over time rather than based on performance. The stock-based compensation expense recorded related to these awards during the years ended December 31, 2023, 2022, and 2021 were immaterial to the Company’s consolidated financial statements. ​ 2015 Stock Option Plan ​ In October 2015, the Company s board of directors and stockholders The 2015 Stock Option Plan replaced the 2014 Plan. Any options or awards outstanding under the 2014 Plan remained outstanding and effective. The number of shares initially reserved for issuance under the 2015 Stock Option Plan is the sum of (a) 1,311,812 shares of common stock and (b) the number of shares under the 2014 Plan that are not needed to fulfill the Company s obligations for awards issued under the 2014 Plan as a result of forfeiture, expiration, cancellation, termination or net issuances of awards thereunder. The number of shares of common stock that may be issued under the 2015 Stock Option Plan is also subject to increase on the first day of each fiscal year by up to 4% of the Company s issued and outstanding shares of common stock on the immediately preceding December 31. ​ Effective January 1, 2016 and every anniversary thereafter an additional 4% of outstanding common stock was added to the Company’s 2015 Stock Option Plan pursuant to its “evergreen” provision, for future issuance. This has accumulated to a total of 12,531,505 shares through January 1, 2024. During the year ended December 31, 2023, the Company granted options to purchase 1,753,800 shares of common stock to employees and directors under the 2015 Stock Option Plan. As of December 31, 2023, there were 3,572,195 shares available for future issuance under the 2015 Stock Option Plan. ​ 2015 Employee Stock Purchase Plan ​ In October 2015, the Company’s board of directors and stockholders approved the 2015 Employee Stock Purchase Plan (the “2015 ESPP”). Under the 2015 ESPP, all full-time employees of the Company are eligible to purchase common stock of the Company twice per year, at the end of each six-month payment period. During each payment period, eligible employees who so elect, may authorize payroll deductions in an amount of 1% to 10% (whole percentages only) of the employee’s base pay for each payroll period. At the end of each payment period, the accumulated deductions are used to purchase shares of common stock from the Company at a discount. A total of 262,362 shares of common stock were initially authorized for issuance under this plan. ​ Effective January 1, 2016 and every anniversary thereafter an additional 1% of outstanding common stock was added to the 2015 ESPP, pursuant to its evergreen provision, for future issuance . This has accumulated to a total of 2,692,838 shares through January 1, 2023. The Company issued 111,639 and 150,265 shares of common stock under the 2015 ESPP in the years ended December 31, 2023 and 2022. As of December 31, 2023, there were 2,158,966 shares available for future purchase under the 2015 ESPP. ​ Inducement Awards ​ In the years ended December 31, 2023, 2022 and, 2021, the Company issued non-statutory stock options to purchase an aggregate of 573,000, 390,000, and 76,500 shares of the Company’s common stock and restricted stock unit awards for an aggregate of 318,500, 163,000, and 13,000 shares of the Company’s common stock, respectively, in each case outside of the Company’s 2015 Stock Option Plan as an inducement material to certain individuals’ acceptance of an offer of employment with the Company in accordance with Nasdaq Listing Rule 5635(c)(4). ​ The stock options will vest over a four-year period, with 25% of the shares underlying the option award vesting on the first anniversary of the award and the remaining 75% of the shares underlying the award vesting monthly thereafter over the subsequent 36-month period. The restricted stock units vest over a three-year period, with 33% of the restricted stock units vesting on the first anniversary of the award, 33% of the restricted stock units vesting on the second anniversary, and the remaining restricted stock units vesting on the third anniversary. ​ Stock-based Compensation Expense ​ Total compensation cost recognized for all stock-based compensation awards in the statements of operations and comprehensive income (loss) is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year ended December 31, ​ 2023 2022 2021 ​ ​ (in thousands) General and administrative ​ $ 7,568 ​ $ 6,398 ​ $ 7,191 ​ Research and development ​ 3,585 ​ 2,946 ​ 4,133 ​ Total stock-based compensation expense ​ $ 11,153 ​ $ 9,344 ​ $ 11,324 ​ ​ Stock-based compensation expense by type of award included within the consolidated statements of operations and ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year ended December 31, ​ ​ ​ 2023 2022 2021 ​ ​ ​ (in thousands) ​ Stock options ​ $ 7,627 ​ $ 5,938 ​ $ 7,438 ​ Restricted stock awards and units ​ ​ 3,241 ​ ​ 3,215 ​ ​ 3,551 ​ Employee stock purchase plan awards ​ 285 ​ 191 ​ 335 ​ Total stock-based compensation expense ​ $ 11,153 ​ $ 9,344 ​ $ 11,324 ​ ​ Restricted Stock Units ​ A summary of the status of and changes in unvested restricted stock unit activity under the Company’s equity award plans for the year ended December 31, 2023 was as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ ​ Average ​ ​ ​ ​ ​ Grant Date ​ ​ ​ ​ ​ Fair Value ​ ​ ​ Units Per Unit ​ Unvested restricted stock units as of December 31, 2022 ​ 1,112,563 ​ $ 5.27 ​ Awarded ​ 999,250 ​ $ 7.58 ​ Vested ​ (531,560) ​ $ 5.73 ​ Forfeited ​ (209,356) ​ $ 6.08 ​ Unvested restricted stock units as of December 31, 2023 ​ 1,370,897 ​ $ 6.65 ​ ​ Stock-based compensation of restricted stock units is based on the fair value of the Company’s common stock on the date of grant and is recognized over the vesting period. In the year ended December 31, 2023, the Company granted 999,250 restricted stock units vesting in equal amounts, annually over three years. The stock-based compensation expense was $3.1 million, $2.9 million, and $3.3 million for the years ended December 31, 2023, 2022, and 2021, respectively. As of December 31, 2023, the Company had unrecognized stock-based compensation expense related to its unvested restricted stock units of $6.8 million which is expected to be recognized over the remaining weighted average vesting period of 1.1 years. ​ Stock Options ​ A summary of the status of, and changes in, stock options was as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted Remaining Aggregate ​ ​ ​ ​ ​ Average ​ Contractual ​ Intrinsic ​ ​ ​ ​ ​ Exercise ​ Life ​ Value ​ ​ ​ Shares Price (in years) (in thousands) ​ Outstanding at December 31, 2022 ​ 6,199,571 ​ $ 8.12 ​ ​ ​ ​ ​ Granted ​ 2,326,800 ​ $ 8.58 ​ ​ ​ ​ ​ ​ Exercised ​ (385,655) ​ $ 4.98 ​ ​ ​ ​ ​ ​ Cancelled or forfeited ​ (715,272) ​ $ 7.86 ​ ​ ​ ​ ​ ​ Outstanding at December 31, 2023 ​ 7,425,444 ​ $ 8.52 ​ 7.3 ​ ​ 11,293 ​ Exercisable at December 31, 2023 ​ 3,823,420 ​ $ 9.43 5.9 ​ $ 6,020 ​ ​ Using the Black-Scholes option pricing model, the weighted average fair value of options granted during the year ended December 31, 2023 was $6.12. The stock-based compensation expense related to stock option awards granted was $7.2 million, $5.8 million, and $7.3 million for the years ended December 31, 2023, 2022, and 2021, respectively. ​ The fair value of each option was estimated at the date of grant using the Black-Scholes option pricing model with the following weighted-average assumptions: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year ended December 31, ​ ​ 2023 2022 2021 ​ Risk-free interest rate 4.0 % 2.2 % 0.9 % ​ Expected dividend yield — % — % — % ​ Expected term (in years) 6.0 ​ 6.0 ​ 6.0 ​ ​ Expected volatility 80.4 % 79.4 % 75.0 % ​ ​ As of December 31, 2023, the Company had unrecognized stock-based compensation expense related to its unvested stock options of $16.6 million which is expected to be recognized over the remaining weighted average vesting period of 2.9 years.

401(k) Savings plan

401(k) Savings plan	12 Months Ended
	Dec. 31, 2023
401(k) Savings plan
401(k) Savings plan	12. 401(k) Savings plan The Company has a defined-contribution savings plan under Section 401(k) of the Internal Revenue Code (the “401(k) Plan”). The 401(k) Plan covers all employees who meet defined minimum age and service requirements, and allows participants to defer a portion of their annual compensation on a pretax basis. The Company expensed approximately $1.1 million, $0.9 million, and $1.1 million related to employer contributions made during the years ended December 31, 2023, 2022, and 2021, respectively.

Income taxes

Income taxes	12 Months Ended
	Dec. 31, 2023
Income taxes
Income taxes	13. Income taxes The Company evaluates its tax positions on an annual basis. The current tax expense recorded for the year ended December 31, 2023 is the residual tax due, after utilization of tax attributes, associated with revenue from collaboration agreements. The provision for incomes taxes is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year ended December 31, ​ 2023 ​ 2022 ​ 2021 ​ (in thousands) ​ ​ ​ Current ​ ​ ​ ​ ​ ​ ​ ​ Federal $ 1,248 ​ $ — ​ $ — State ​ 160 ​ ​ 16 ​ ​ — Total current ​ 1,408 ​ ​ 16 ​ ​ — ​ ​ ​ ​ ​ ​ ​ ​ ​ Deferred ​ ​ ​ ​ ​ ​ ​ ​ Federal ​ — ​ ​ — ​ ​ — State ​ — ​ ​ — ​ ​ — Total deferred ​ — ​ ​ — ​ ​ — Total tax provision $ 1,408 ​ $ 16 ​ $ — ​ A reconciliation of the expected income tax provision computed using the federal statutory income tax rate at the Company’s effective tax rate for the years ended December 31, 2023, 2022, and 2021 is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year ended December 31, ​ ​ 2023 ​ 2022 ​ 2021 ​ Income tax computed at federal statutory tax rate ​ 21.0 % ​ 21.0 % ​ 21.0 % ​ State taxes, net of federal benefit ​ 5.4 % ​ 5.2 % ​ 6.6 % ​ Provision to return ​ 0.9 % ​ 3.2 % ​ 4.9 % ​ General business credit carryovers ​ (0.4) % ​ (3.5) % ​ 3.2 % ​ Non-deductible expenses ​ 0.5 % ​ (4.6) % ​ (3.8) % ​ Other ​ (0.4) % ​ — % ​ — % ​ Change in valuation allowance ​ (26.0) % ​ (21.3) % ​ (31.9) % ​ Total ​ 1.00 % ​ — % ​ — % ​ ​ The Company has historically incurred net operating losses (“NOLs”). As of December 31, 2023, the Company had federal and state net operating loss carryforwards of $55.3 million and $33.2 million, respectively. As of December 31, 2023, the Company had federal and state research and development tax credit carryforwards of $19.6 million and $10.8 million, respectively, which expire beginning in 2033. As of December 31, 2022, the Company had state investment credits of $0.4 million, which expire beginning in 2024. ​ The significant components of the Company’s deferred tax assets and (liabilities) as of December 31, 2023 and 2022 are as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ ​ 2023 ​ 2022 ​ (in thousands) ​ Deferred tax assets: ​ ​ ​ ​ ​ ​ Net operating loss carryforward $ 13,724 ​ $ 47,282 ​ Tax credit carryforward 28,427 ​ 32,060 ​ Lease liability ​ 5,544 ​ ​ 6,318 ​ Deferred revenue ​ 1,675 ​ ​ 17,984 ​ Stock compensation ​ 5,157 ​ ​ 4,630 ​ Non-deductible accruals and reserves 2,613 ​ 1,603 ​ Capitalized research expenses ​ 31,347 ​ ​ 14,351 ​ Intangibles 554 ​ 610 ​ Other temporary differences ​ — ​ ​ (1) ​ Total deferred tax assets 89,041 ​ 124,837 ​ Less valuation allowance (82,612) ​ (117,416) ​ Net deferred tax assets 6,429 ​ 7,421 ​ Deferred tax liabilities ​ ​ ​ ​ ​ Right of use assets ​ (3,691) ​ (4,231) ​ Depreciation and amortization ​ (2,738) ​ ​ (3,190) ​ Other temporary differences ​ — ​ ​ — ​ Net deferred taxes $ — ​ $ — ​ ​ As required by ASC 740, management has evaluated the positive and negative evidence bearing upon the realizability of its deferred tax assets, which principally comprise NOL carryforwards, tax credit carryforwards, and capitalized research expenses. Management has determined that it is more likely than not that the Company will not recognize the benefits of its federal and state deferred tax assets, and as a result, a valuation allowance of $82.6 million and $117.4 million has been established at December 31, 2023 and 2022, respectively. The state NOLs will expire beginning in 2041 while the federal NOLs do not expire. The valuation allowance decreased by $34.8 million for the year ended December 31, 2023 primarily as a result of the utilization of the NOL carryforwards and tax credits in 2023. ​ At December 31, 2023 and 2022, the Company had no unrecognized tax benefits. The Company is in the process of completing a study of its research and development credit carryforwards. The Company has recorded an adjustment in the current year to reflect the preliminary results of the research and development study. The completion of the study may result in an additional adjustment to the Company’s research and development credit carryforwards; however, until a study is completed, no amounts are being presented as an uncertain tax position. A full valuation allowance has been provided against the Company’s research and development credits, and if an adjustment is required, this adjustment would be offset by an adjustment to the valuation allowance. Thus, there would be no impact to the balance sheets or statements of operations and comprehensive income (loss) if an adjustment were required. ​ Interest and penalty charges, if any, related to unrecognized tax benefits would be classified as income tax expense in the accompanying statements of operations. As of December 31, 2023 and 2022, the Company has no accrued interest related to uncertain tax positions. Since the Company is in a loss carryforward position, it is generally subject to examination by the U.S. federal, state, and local income tax authorities for all tax years in which a loss carryforward is available.

Related party transactions

Related party transactions	12 Months Ended
	Dec. 31, 2023
Related party transactions
Related party transactions	14. Related-party transactions ​ During the years ended December 31, 2023, 2022, and 2021, the Company received scientific advisory services from one of its prior executives, Dinah Sah, Ph.D., the Company’s former Chief Scientific Officer. The total amount of fees paid to Dr. Sah for services provided during the years ended December 31, 2023, 2022 and 2021 was $0.7 million, $0.5 million, and $0.2 million, respectively. ​ During the year ended December 31, 2022, the Company received advisory services related to strategic planning, operations, and management from Alfred Sandrock, M.D., Ph.D., the Company’s current President and Chief Executive Officer and a member of the Company’s board of directors, before he commenced service in the capacity of President and Chief Executive Officer in March 2022. The total amount of fees paid to Dr. Sandrock for services provided was $60,000 for the year ended December 31, 2022. ​ Under both the 2019 Neurocrine Collaboration Agreement and the 2023 Neurocrine Collaboration Agreement, the Company and Neurocrine have agreed to conduct research, development and commercialization activities for certain of the Company’s AAV gene therapy products (Note 9). Amounts due from Neurocrine are reflected as related party collaboration receivable. As of December 31, 2023, the Company recorded approximately $3.3 million in related party collaboration receivable relative to the 2019 Neurocrine Collaboration Agreement and the 2023 Neurocrine Collaboration Agreement.

Subsequent events

Subsequent events	12 Months Ended
	Dec. 31, 2023
Subsequent events
Subsequent events	15. Subsequent events ​ On January 4, 2024, the Company entered into an underwriting agreement (the “Underwriting Agreement”) with Citigroup Global Markets Inc. and Guggenheim Securities, LLC, as representatives of the several underwriters named therein (the “Underwriters”), relating to an underwritten public offering of 7,777,778 shares of the Company’s common stock, par value $0.001 per share, and, in lieu of common stock to certain investors, pre-funded warrants (the “Pre-Funded Warrants”) to purchase up to 3,333,333 shares of common stock. The public offering price of the Company’s common stock was $9.00 per share, and the public offering price of the Pre-Funded Warrants was $8.999 per share underlying each Pre-Funded Warrant. The Underwriters have agreed to purchase the Company’s stock from the Company pursuant to the Underwriting Agreement at a price of $8.46 and the Pre-Funded Warrants from the Company pursuant to the Underwriting Agreement at a price of $8.459 per share underlying each Pre-Funded Warrant. Under the terms of the Underwriting Agreement, the Company also granted the Underwriters an option, exercisable for 30 days, to purchase up to an additional 1,666,665 shares of common stock at the public offering price less the underwriting discounts and commissions. This option was not exercised during the thirty-day exercise period, and the option expired on February 2, 2024. ​ The Company received net proceeds from the public offering of approximately $93.5 million after deducting underwriting discounts and commissions and estimated offering expenses. ​ The Company and Novartis entered into a stock purchase agreement (“the 2023 Novartis Stock Purchase Agreement”) on December 28, 2023, for the sale and issuance of 2,145,002 shares of the Company’s common stock (the “Novartis Shares”) to Novartis at a price of $9.324 per share, for an aggregate purchase price of approximately $20.0 million. In accordance with the terms and conditions of the 2023 Novartis Stock Purchase Agreement, the Company issued and sold the Novartis Shares to Novartis on January 3, 2024. ​ In February 2024, the Company announced that the joint steering committee with its collaborator Neurocrine selected a lead development candidate for the FA Program, which triggered a $5.0 million milestone payment to the Company. The Company expects to receive the $5.0 million during the first quarter of 2024. ​ ​

Summary of significant accoun_2

Summary of significant accounting policies and basis of presentation (Policies)	12 Months Ended
	Dec. 31, 2023
Summary of significant accounting policies and basis of presentation
Basis of Presentation	Basis of presentation ​ The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”) and pursuant to the rules and regulations of the U.S. Securities and Exchange Commission (“SEC”) for reporting on Form 10-K. The Company’s consolidated financial statements include the accounts of Voyager Therapeutics, Inc. and its wholly-owned subsidiary, Voyager Securities Corporation. All intercompany balances and transactions have been eliminated. ​
Use of Estimates	Use of Estimates ​ The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. On an ongoing basis, the Company’s management evaluates its estimates, which include, but are not limited to, estimates related to revenue recognition, research and development accrued expenses, stock-based compensation expense, and income taxes. The Company bases its estimates on historical experience and other market specific or other relevant assumptions that it believes to be reasonable under the circumstances. Actual results may differ from those estimates or assumptions.
Fair Value of Financial Instruments	​ Fair Value of Financial Instruments ​ ASC Topic 820, Fair Value Measurement ​ ASC 820 identifies fair value as the exchange price, or exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As a basis for considering market participant assumptions in fair value measurements, ASC 820 establishes a three-tier fair value hierarchy that distinguishes between the following: ​ ● Level 1 —Quoted market prices in active markets for identical assets or liabilities. ● Level 2 —Inputs other than Level 1 inputs that are either directly or indirectly observable, such as quoted market prices, interest rates, and yield curves. ● Level 3 —Unobservable inputs developed using estimates of assumptions developed by the Company, which reflect those that a market participant would use. ​ To the extent that the valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. ​ The carrying amounts reflected in the balance sheets for cash and cash equivalents, prepaid expenses and other current assets, accounts payable and accrued expenses approximate their fair values, due to their short-term nature. ​
Cash and Cash Equivalents	Cash and Cash Equivalents ​ The Company considers all highly liquid investments purchased with original maturities of 90 days or less at acquisition to be cash equivalents. Cash and cash equivalents include cash held in banks and amounts held in money market funds. ​
Marketable Securities	Marketable Securities ​ The Company classifies marketable securities with a remaining maturity of greater than three months when purchased as available-for-sale. Marketable securities with a remaining maturity date greater than one year are classified as non-current where the Company has the intent and ability to hold these securities for at least the next 12 months. ​ All available-for-sale debt securities are carried at fair value with the unrealized gains and losses included in other comprehensive income (loss) as a component of stockholders’ equity until realized. Any premium or discount arising at purchase is amortized and/or accreted to interest income and/or expense. Realized gains and losses are determined using the specific identification method and are included in other income. If any adjustment to fair value reflects a decline in value of the investment, the Company uses a forward-looking approach based on expected losses to estimate credit losses on certain types of financial instruments, including trade receivables and available-for-sale debt securities. No other than temporary losses or credit losses have been recognized. ​ Cash, cash equivalents, and marketable securities as of December 31, 2023 and 2022 consist of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Amortized ​ Unrealized ​ Unrealized ​ Fair ​ Cost Gains Losses Value ​ ​ (in thousands) As of December 31, 2023 ​ ​ ​ ​ ​ ​ Money market funds included in cash and cash equivalents $ 65,589 ​ ​ — ​ ​ — ​ $ 65,589 ​ Marketable securities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ U.S. Treasury notes ​ ​ 102,966 ​ ​ 81 ​ ​ (3) ​ ​ 103,044 ​ U.S. Government agency securities ​ ​ 31,068 ​ ​ 10 ​ ​ (3) ​ ​ 31,075 ​ Corporate bonds ​ ​ 23,975 ​ ​ 2 ​ ​ (7) ​ ​ 23,970 ​ Commercial paper ​ ​ 3,985 ​ ​ — ​ ​ — ​ ​ 3,985 ​ Total money market funds and marketable securities $ 227,583 ​ $ 93 ​ $ (13) ​ $ 227,663 ​ As of December 31, 2022 ​ ​ ​ ​ ​ Money market funds included in cash and cash equivalents $ 91,724 ​ $ — ​ $ — ​ $ 91,724 ​ Marketable securities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ U.S. Treasury notes ​ 19,980 ​ ​ — ​ ​ (91) ​ ​ 19,889 ​ Total money market funds and marketable securities $ 111,704 ​ $ — ​ $ (91) ​ $ 111,613 ​ ​ All of the Company’s marketable securities at December 31, 2023 and 2022 have a contractual maturity of one year or less. ​ The Company reviews investments whenever the fair value of an investment is less than the amortized cost and evidence indicates that an investment’s carrying amount is not recoverable within a reasonable period of time. In connection with these investments, the Company evaluates whether the decline in fair value has resulted from credit losses or other factors, considering the extent to which fair value is less than amortized cost, any changes to the rating of the security by a rating agency, and adverse conditions specifically related to the security, among other factors. If this assessment indicates that a credit loss exists, the present value of cash flows expected to be collected from the security is compared to the amortized cost basis of the security. If the present value of cash flows expected to be collected is less than the amortized cost basis, a credit loss exists and an allowance for credit losses is recorded for the credit loss on the condensed consolidated balance sheet, limited by the amount that the fair value is less than the amortized cost basis. Any impairment that is not related to credit is recognized in other comprehensive income (loss). Changes in the allowance for credit losses are recorded as a provision for (or reversal of) credit loss expense in general and administrative expenses within the consolidated statement of operations and comprehensive income (loss). Losses are charged against the allowance when the Company believes the uncollectability of an available-for-sale security is confirmed or when either of the criteria regarding intent or requirement to sell is met. ​ The Company held $44.2 million and $19.9 million in marketable securities that were in an unrealized loss position as of December 31, 2023 and December 31, 2022, respectively. The unrealized losses at December 31, 2023 and December 31, 2022 were attributable to changes in interest rates and the unrealized losses do not represent credit losses. The Company does not intend to sell these securities and it is not more likely than not that it will be required to sell them before recovery of their amortized cost basis. ​
Restricted Cash	Restricted Cash ​ As of December 31, 2023 and 2022, the Company maintained restricted cash totaling approximately $1.6 million and $1.5 million, respectively, held in the form of money market accounts as collateral for the Company’s facility lease obligations. The balance is included within deposits and other non-current assets in the accompanying consolidated balance sheets. The following table provides a reconciliation of cash, cash equivalents, and restricted cash within the consolidated balance sheets that sum to the total of the same such amounts shown in the statements of cash flows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ ​ ​ 2023 2022 2021 ​ ​ ​ (in thousands) ​ Cash and cash equivalents ​ $ 68,802 ​ $ 98,959 ​ $ 117,433 ​ Restricted cash included in deposits and other non-current assets ​ ​ 1,593 ​ ​ 1,515 ​ ​ 1,779 ​ Total cash, cash equivalents, and restricted cash ​ $ 70,395 ​ $ 100,474 ​ $ 119,212 ​ ​
Property and Equipment	Property and Equipment ​ Property and equipment consists of laboratory equipment, furniture and office equipment, and leasehold improvements and is stated at cost, less accumulated depreciation. Maintenance and repairs that do not improve or extend the lives of the respective assets are expensed to operations as incurred; while costs of major additions and betterments are capitalized. Depreciation is calculated over the estimated useful lives of the assets using the straight-line method. ​
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets ​ The Company evaluates long-lived assets for potential impairment when events or changes in circumstances indicate the carrying value of the assets may not be recoverable. Recoverability is measured by comparing the book values of the assets to the expected future net undiscounted cash flows that the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the book values of the assets exceed their fair value. The Company has not recognized any impairment losses from inception through December 31, 2023. ​
Revenue Recognition	Revenue Recognition ​ The Company enters into license, option, and collaboration agreements which are within the scope of ASC 606, Revenue from Contracts with Customers ​ The promised goods or services in the Company’s arrangements typically consist of license rights to the Company’s intellectual property and research and development services. The Company provides options to additional items in the contracts, which are accounted for as separate contracts when the customer elects to exercise such options, unless the option provides a material right to the customer. The Company evaluates the customer options for material rights, or options to acquire additional goods or services for free or at a discount. If the customer options are determined to represent a material right, the material right is recognized as a separate performance obligation at the outset of the arrangement. Performance obligations are promised goods or services in a contract to transfer a distinct good or service to the customer and are considered distinct when (a) the customer can benefit from the good or service on its own or together with other readily available resources and (b) the promised good or service is separately identifiable from other promises in the contract. In assessing whether promised goods or services are distinct, the Company considers factors such as the stage of development of the underlying intellectual property, the capabilities of the customer to develop the intellectual property on its own or whether the required expertise is readily available and whether the goods or services are integral or dependent to other goods or services in the contract. ​ The Company estimates the transaction price based on the amount expected to be received for transferring the promised goods or services in the contract. The consideration may include fixed consideration or variable consideration. At the inception of each arrangement that includes variable consideration, the Company evaluates the amount of potential payments and the likelihood that the payments will be received. The Company utilizes either the most likely amount method or expected amount method to estimate the amount expected to be received based on which method best predicts the amount expected to be received. The amount of variable consideration which is included in the transaction price may be constrained, and is included in the transaction price only to the extent that it is probable that a significant reversal in the amount of the cumulative revenue recognized will not occur in a future period. ​ The Company’s contracts often include development and regulatory milestone payments which are assessed under the most likely amount method and constrained if it is probable that a significant revenue reversal would occur. Milestone payments that are not within the Company’s control or the licensee’s control, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. At the end of each reporting period, the Company re-evaluates the probability of achievement of such development milestones and any related constraint, and if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect collaboration revenue in the period of adjustment. To date, the Company has not recognized any consideration related to the achievement of development, regulatory, or commercial milestone revenue resulting from any of the Company’s collaboration or license arrangements. ​ For arrangements that include sales-based royalties, including milestone payments based on the level of sales, in which the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (a) when the related sales occur, or (b) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has not recognized any consideration related to sales-based royalty revenue resulting from any of the Company’s collaboration or license arrangements. ​ The Company allocates the transaction price based on the estimated stand-alone selling price of each of the performance obligations. The Company must develop assumptions that require judgment to determine the stand-alone selling price for each performance obligation identified in the contract. The Company utilizes key assumptions to determine the stand-alone selling price for service obligations, which may include other comparable transactions, pricing considered in negotiating the transaction and the estimated costs. Additionally, in determining the standalone selling price for material rights, the Company utilizes comparable transactions, clinical trial success probabilities, and estimates of option exercise likelihood. Variable consideration is allocated specifically to one or more performance obligations in a contract when the terms of the variable consideration relate to the satisfaction of the performance obligation and the resulting amounts allocated are consistent with the amounts the Company would expect to receive for the satisfaction of each performance obligation. ​ The consideration allocated to each performance obligation is recognized as revenue when control is transferred for the related goods or services. For performance obligations which consist of licenses and other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. ​ Upfront payments and fees are recorded as contract liabilities within deferred revenue on the consolidated balance sheets until the Company performs its obligations under these arrangements. Amounts are recorded as accounts receivable when the Company’s right to consideration is unconditional. A portion of revenue recognized from the 2019 and 2023 Neurocrine Collaboration Agreements and the 2023 Novartis Collaboration Agreement is related to performance obligations pursuant to which revenue is recognized using a proportional performance model. Revenue is recognized using input-based measurements, which involves the measurement of progress toward each performance obligation based on the actual costs incurred compared to total projected costs. The Company estimates the expected remaining costs to complete the research and development services for each performance obligation. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure and related revenue recognition. ​
Research and Development	Research and Development ​ Research and development costs are charged to expense as incurred in performing research and development activities. The costs include employee compensation costs, external research, consultant costs, sponsored research, license fees, process development and facilities costs. Facilities costs primarily include the allocation of rent, utilities and depreciation. ​
Leases	Leases ​ The Company determines if an arrangement is or contains a lease at inception under Accounting Standards Codification (ASC) 842 Leases ​ Right-of-use assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. Operating lease right-of-use assets and liabilities are recognized at the lease commencement date based on the present value of lease payments over the lease term. As the Company’s leases typically do not provide an implicit rate, the Company uses an estimate of its incremental borrowing rate based on the information available at the lease commencement date in determining the present value of lease payments. Operating lease right-of-use assets also include the effect of any lease prepaid or deferred lease payments and are reduced by lease incentives. The lease terms may include options to extend or terminate the lease when it is reasonably certain that the Company will exercise that option. Lease expense is recognized on a straight-line basis over the lease term. ​ The Company has lease agreements with lease and non-lease components, which are generally accounted for separately. Non-lease components as it pertains to the Company's leased premises generally refer to common area maintenance charges related to the premises. ​
Research Contract Costs and Accruals	Research Contract Costs and Accruals ​ The Company has entered into various research and development contracts with research institutions and other companies. These agreements are generally cancelable. The Company records accruals for estimated ongoing research costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates may be made in determining the accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates. The Company’s historical accrual estimates have not been materially different from the actual costs. ​
Patent Costs	Patent Costs ​ The Company expenses patent application and related legal costs as incurred and classifies such costs as general and administrative expenses in the accompanying statements of operations. ​
Stock-Based Compensation Expense	Stock-Based Compensation Expense ​ The Company accounts for its stock-based compensation awards in accordance with ASC Topic 718 Compensation—Stock Compensation ​ The Black-Scholes option pricing model requires inputs based on certain subjective assumptions, including (a) the expected stock price volatility, (b) the expected term of the award, (c) the risk-free interest rate and (d) expected dividends. The Company bases the estimate of expected volatility on the historical volatility of its common stock. The historical volatility is calculated based on a period of time commensurate with the expected term assumption. The Company uses the simplified method as prescribed by the SEC Staff Accounting Bulletin No. 107, Share-Based Payment ​ The Company expenses the fair value of its stock-based compensation awards on a straight-line basis over the associated service period, which is generally the period in which the related services are received, adjusted for actual forfeitures of unvested awards as they occur. ​ The Company records the expense for stock-based compensation awards subject to performance conditions over the remaining service period when management determines that achievement of the performance condition is probable. Management evaluates when the achievement of a performance condition is probable based on the expected satisfaction of the performance conditions as of the reporting date. ​
Income Taxes	Income Taxes ​ Income taxes are recorded in accordance with ASC Topic 740, Income Taxes reverse. The Company provides a valuation allowance against net deferred tax assets unless, based upon the weight of available evidence, it is more likely than not that the deferred tax assets will be realized. ​ The Company accounts for uncertain tax positions in accordance with the provisions of ASC 740. When uncertain tax positions exist, the Company recognizes the tax benefit of tax positions to the extent that the benefit will more likely than not be realized. The determination as to whether the tax benefit will more likely than not be realized is based upon the technical merits of the tax position as well as consideration of the available facts and circumstances. As of December 31, 2023, the Company does not have any significant uncertain tax positions. ​
Comprehensive Income (Loss)	Comprehensive Income (Loss) ​ Comprehensive income (loss) is comprised of net income (loss) and other comprehensive income or loss. Other comprehensive income or loss consists of unrealized gains or losses on marketable securities. ​
Net Income (Loss) Per Share	Net Income (Loss) Per Share ​ Basic net income (loss) per share is calculated by dividing the net income (loss) by the weighted-average number of shares of common stock outstanding during the period, without consideration for potentially dilutive securities. Diluted net income (loss) per share is computed by dividing the net income (loss) by the weighted-average number of shares of common stock and potentially dilutive securities outstanding for the period determined using the treasury-stock and if-converted methods. ​ For purposes of the diluted net income (loss) per share, unvested restricted common stock and outstanding stock options are considered to be potentially dilutive securities. Unvested restricted common stock and outstanding stock options were excluded from the calculation of diluted net loss per share in the years ended December 31, 2023 and 2022, because their effect would be anti-dilutive and therefore, basic and diluted net loss per share were the same for the years ended December 31, 2023 and 2022. ​ The following table sets forth the outstanding potentially dilutive securities that have been excluded in the calculation of diluted net income (loss) per share because to do so would be anti-dilutive: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ ​ ​ 2023 ​ 2022 ​ 2021 ​ Unvested restricted common stock awards ​ 22,500 ​ 45,000 ​ 137,255 ​ Unvested restricted common stock units ​ ​ 1,370,897 ​ ​ 1,112,563 ​ ​ 806,379 ​ Outstanding stock options ​ 7,425,444 ​ 6,199,571 ​ 5,013,193 ​ Total ​ 8,818,841 ​ 7,357,134 ​ 5,956,827 ​ ​ Basic net income (loss) and diluted weighted-average shares outstanding are as follows for the years ended December 31, 2023, 2022, and 2021: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ ​ ​ 2023 ​ 2022 ​ 2021 ​ ​ ​ (in thousands, except share data) ​ Numerator: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net income (loss) ​ $ 132,330 ​ $ (46,408) ​ $ (71,197) ​ Denominator for basic net income (loss) per share: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted average shares outstanding-basic ​ ​ 43,020,747 ​ ​ 38,356,810 ​ ​ 37,668,947 ​ Denominator for diluted net income (loss) per share: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted average shares outstanding ​ ​ 43,020,747 ​ ​ 38,356,810 ​ ​ 37,668,947 ​ Common stock options and restricted stock units ​ ​ 1,548,587 ​ ​ — ​ ​ — ​ Weighted average shares outstanding-diluted ​ ​ 44,569,334 ​ ​ 38,356,810 ​ ​ 37,668,947 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​
Concentrations of Credit Risk and Significant Suppliers	Concentrations of Credit Risk and Significant Suppliers ​ The Company has no financial instruments with off-balance sheet risk such as foreign exchange contracts, option contracts or other foreign currency hedging arrangements. Financial instruments that potentially subject the Company to a concentration of credit risk are cash and cash equivalents. The Company’s cash is held in accounts at financial institutions that may exceed federally insured limits. The Company has not experienced any credit losses in such accounts and does not believe it is exposed to any significant credit risk on these funds. ​ The Company is dependent on third-party manufacturers to supply certain products for research and development activities in its programs. In particular, the Company relies on a sole manufacturer to supply it with specific vectors related to the Company’s research and development programs. ​
Segment Information	Segment Information ​ Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker (“CODM”) in deciding how to allocate resources and assess performance. The Company and the Company’s CODM, the Company’s Chief Executive Officer, view the Company’s operations and manages its business as a single operating segment, which is the business of developing and commercializing genetic medicine.
Recent Accounting Pronouncements	Recent Accounting Pronouncements ​ In August 2020, the Financial Accounting Standards Board (“FASB”) issued ASU No. 2020-06, Debt – Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging—Contracts in Entity’s Own Equity (Subtopic 815-40) ​ In November 2023 the FASB issued ASU No. 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosure ​ In December 2023, the FASB issued ASU 2023-09, “ Income Taxes (Topic 740) - Improvements to Income Tax Disclosures.”

Summary of significant accoun_3

Summary of significant accounting policies and basis of presentation (Tables)	12 Months Ended
	Dec. 31, 2023
Summary of significant accounting policies and basis of presentation
Schedule of money market funds and marketable securities	Cash, cash equivalents, and marketable securities as of December 31, 2023 and 2022 consist of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Amortized ​ Unrealized ​ Unrealized ​ Fair ​ Cost Gains Losses Value ​ ​ (in thousands) As of December 31, 2023 ​ ​ ​ ​ ​ ​ Money market funds included in cash and cash equivalents $ 65,589 ​ ​ — ​ ​ — ​ $ 65,589 ​ Marketable securities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ U.S. Treasury notes ​ ​ 102,966 ​ ​ 81 ​ ​ (3) ​ ​ 103,044 ​ U.S. Government agency securities ​ ​ 31,068 ​ ​ 10 ​ ​ (3) ​ ​ 31,075 ​ Corporate bonds ​ ​ 23,975 ​ ​ 2 ​ ​ (7) ​ ​ 23,970 ​ Commercial paper ​ ​ 3,985 ​ ​ — ​ ​ — ​ ​ 3,985 ​ Total money market funds and marketable securities $ 227,583 ​ $ 93 ​ $ (13) ​ $ 227,663 ​ As of December 31, 2022 ​ ​ ​ ​ ​ Money market funds included in cash and cash equivalents $ 91,724 ​ $ — ​ $ — ​ $ 91,724 ​ Marketable securities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ U.S. Treasury notes ​ 19,980 ​ ​ — ​ ​ (91) ​ ​ 19,889 ​ Total money market funds and marketable securities $ 111,704 ​ $ — ​ $ (91) ​ $ 111,613 ​
Reconciliation of cash, cash equivalents, and restricted cash	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ ​ ​ 2023 2022 2021 ​ ​ ​ (in thousands) ​ Cash and cash equivalents ​ $ 68,802 ​ $ 98,959 ​ $ 117,433 ​ Restricted cash included in deposits and other non-current assets ​ ​ 1,593 ​ ​ 1,515 ​ ​ 1,779 ​ Total cash, cash equivalents, and restricted cash ​ $ 70,395 ​ $ 100,474 ​ $ 119,212 ​
Outstanding potentially dilutive securities excluded in the calculation of diluted net income (loss) per share	The following table sets forth the outstanding potentially dilutive securities that have been excluded in the calculation of diluted net income (loss) per share because to do so would be anti-dilutive: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ ​ ​ 2023 ​ 2022 ​ 2021 ​ Unvested restricted common stock awards ​ 22,500 ​ 45,000 ​ 137,255 ​ Unvested restricted common stock units ​ ​ 1,370,897 ​ ​ 1,112,563 ​ ​ 806,379 ​ Outstanding stock options ​ 7,425,444 ​ 6,199,571 ​ 5,013,193 ​ Total ​ 8,818,841 ​ 7,357,134 ​ 5,956,827 ​ ​
Schedule of weighted average number of shares, basic and diluted	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ ​ ​ 2023 ​ 2022 ​ 2021 ​ ​ ​ (in thousands, except share data) ​ Numerator: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net income (loss) ​ $ 132,330 ​ $ (46,408) ​ $ (71,197) ​ Denominator for basic net income (loss) per share: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted average shares outstanding-basic ​ ​ 43,020,747 ​ ​ 38,356,810 ​ ​ 37,668,947 ​ Denominator for diluted net income (loss) per share: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted average shares outstanding ​ ​ 43,020,747 ​ ​ 38,356,810 ​ ​ 37,668,947 ​ Common stock options and restricted stock units ​ ​ 1,548,587 ​ ​ — ​ ​ — ​ Weighted average shares outstanding-diluted ​ ​ 44,569,334 ​ ​ 38,356,810 ​ ​ 37,668,947 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Fair value measurements (Tables

Fair value measurements (Tables)	12 Months Ended
	Dec. 31, 2023
Fair value measurements
Assets and liabilities measured at fair value on a recurring basis	Assets and liabilities measured at fair value on a recurring basis as of December 31, 2023 and 2022 are as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Quoted Prices ​ Significant ​ ​ ​ ​ ​ ​ ​ ​ in Active ​ Other ​ Significant ​ ​ ​ ​ ​ Markets for ​ Observable ​ Unobservable ​ ​ ​ ​ ​ Identical Assets ​ Inputs ​ Inputs ​ Assets Total (Level 1) (Level 2) (Level 3) ​ ​ (in thousands) December 31, 2023 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds included in cash and cash equivalents ​ $ 65,589 ​ $ 65,589 ​ $ — ​ $ — ​ Marketable securities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ U.S. Treasury notes ​ ​ 103,044 ​ ​ 103,044 ​ ​ — ​ ​ — ​ U.S. Government agency securities ​ ​ 31,075 ​ ​ 31,075 ​ ​ — ​ ​ — ​ Corporate bonds ​ ​ 23,970 ​ ​ — ​ ​ 23,970 ​ ​ — ​ Commercial paper ​ ​ 3,985 ​ ​ — ​ ​ 3,985 ​ ​ — ​ Total money market funds and marketable securities ​ $ 227,663 ​ $ 199,708 ​ $ 27,955 ​ $ — ​ December 31, 2022 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds included in cash and cash equivalents $ 91,724 ​ $ 91,724 ​ $ — $ — ​ Marketable securities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ U.S. Treasury notes ​ 19,889 ​ ​ 19,889 ​ ​ — ​ ​ — ​ Total money market funds and marketable securities $ 111,613 ​ $ 111,613 ​ $ — ​ $ — ​

Prepaid expenses and other cu_2

Prepaid expenses and other current assets (Tables)	12 Months Ended
	Dec. 31, 2023
Prepaid expense and other current assets
Schedule of prepaid expense and other current assets	Prepaid expenses and other current assets consist of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ 2023 2022 ​ ​ (in thousands) ​ Other current assets ​ $ 2,628 ​ $ 4,233 ​ Prepaid insurance ​ 607 ​ 696 ​ Prepaid research and development contracts 1,119 ​ ​ 83 ​ Accrued interest receivable ​ ​ 964 ​ ​ 382 ​ Total ​ $ 5,318 ​ $ 5,394 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Property and equipment, net (Ta

Property and equipment, net (Tables)	12 Months Ended
	Dec. 31, 2023
Property and equipment, net
Schedule of property and equipment, net	Property and equipment, net consists of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ ​ 2023 2022 ​ ​ (in thousands) ​ Laboratory equipment ​ $ 20,536 ​ $ 19,675 ​ Leasehold improvements ​ ​ 7,106 ​ ​ 12,554 ​ Furniture and office equipment ​ 2,625 ​ 2,333 ​ Other ​ ​ 1,265 ​ 502 ​ Total property and equipment ​ 31,532 ​ 35,064 ​ Less: accumulated depreciation ​ (15,038) ​ (17,207) ​ Property and equipment, net ​ $ 16,494 ​ $ 17,857 ​

Accrued expenses (Tables)

Accrued expenses (Tables)	12 Months Ended
	Dec. 31, 2023
Accrued expenses
Schedule of accrued expenses	Accrued expenses consist of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ ​ 2023 2022 ​ ​ (in thousands) ​ Employee compensation costs ​ $ 6,614 ​ $ 4,559 ​ Research and development costs ​ ​ 5,225 ​ ​ 1,895 ​ Accrued goods and services ​ 4,229 ​ 636 ​ Professional services ​ 755 ​ 726 ​ Total ​ $ 16,823 ​ $ 7,816 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Lease obligation (Tables)

Lease obligation (Tables)	12 Months Ended
	Dec. 31, 2023
Lease obligation
Summary of operating sublease income	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Years ended ​ December 31, ​ 2023 2022 ​ 2021 ​ (in thousands) Operating sublease income $ — ​ $ 1,380 ​ $ 838 ​

Commitments, contingencies, a_2

Commitments, contingencies, and other liabilities (Tables)	12 Months Ended
	Dec. 31, 2023
Commitments, contingencies, and other liabilities
Summary of other current and non-current liabilities	​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ ​ 2023 2022 ​ ​ (in thousands) ​ Other current liabilities ​ ​ ​ ​ ​ ​ Lease liabilities ​ 3,200 ​ ​ 2,832 ​ Total other current liabilities $ 3,200 ​ $ 2,832 ​ ​ ​ ​ ​ ​ ​ ​ Other non-current liabilities ​ ​ ​ ​ ​ ​ Lease liabilities $ 17,093 ​ $ 20,294 ​ Other ​ 1,001 ​ ​ 1,001 ​ Total other non-current liabilities $ 18,094 ​ $ 21,295 ​

Significant Agreements (Tables)

Significant Agreements (Tables)	12 Months Ended
	Dec. 31, 2023
Neurocrine Collaborative Agreement 2023
Schedule of allocation of variable consideration	​ ​ ​ ​ ​ Performance Obligation ​ Amount ​ ​ (in thousands) Variable Consideration ​ ​ GBA1 Program ​ $ 5,920 2023 Discovery Program 1 ​ ​ 3,779 2023 Discovery Program 2 ​ ​ 780 2023 Discovery Program 3 ​ ​ 780 Total ​ $ 11,259
Schedule of allocation of fixed consideration	​ ​ ​ ​ ​ Performance Obligation ​ Amount ​ ​ (in thousands) Fixed Consideration ​ ​ GBA1 Program ​ $ 69,459 2023 Discovery Program 1 ​ ​ 24,807 2023 Discovery Program 2 ​ ​ 24,807 2023 Discovery Program 3 ​ ​ 24,807 Total ​ $ 143,880
Neurocrine Collaborative Agreement 2019
Schedule of allocation of variable consideration	​ ​ ​ ​ ​ ​ Performance Obligation ​ Amount ​ ​ ​ (in thousands) ​ Variable Consideration ​ ​ ​ VY-AADC Program ​ $ 53,863 ​ FA Program ​ ​ 20,309 ​ 2019 Discovery Program 1 ​ ​ 4,286 ​ 2019 Discovery Program 2 ​ ​ 4,793 ​ Total ​ $ 83,251 ​
Schedule of allocation of fixed consideration	​ ​ ​ ​ ​ ​ Performance Obligation ​ Amount ​ ​ ​ (in thousands) ​ Fixed Consideration ​ ​ ​ VY-AADC Program ​ $ 49,045 ​ FA Program ​ ​ 20,647 ​ 2019 Discovery Program 1 ​ ​ 14,443 ​ 2019 Discovery Program 2 ​ ​ 8,247 ​ Total ​ $ 92,382 ​
Neurocrine collaborative Agreement 2023 and Neurocrine Collaborative Agreement 2019
Schedule of collaboration receivables and contract liabilities	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balance at ​ ​ ​ ​ Balance at ​ ​ December 31, 2022 ​ Additions ​ Deductions ​ December 31, 2023 ​ ​ ​ ( in thousands) Related party collaboration receivable ​ $ 257 ​ $ 10,081 ​ $ (6,997) ​ $ 3,341 Contract liabilities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Deferred revenue ​ $ 11,827 ​ $ 74,420 ​ $ (11,007) ​ $ 75,240

Common stock (Tables)

Common stock (Tables)	12 Months Ended
	Dec. 31, 2023
Common stock.
Schedule of shares reserved for future issuance	​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ ​ 2023 2022 Shares reserved for vesting of restricted stock awards under the Founder Agreements 22,500 ​ 45,000 ​ Shares reserved for exercise of outstanding stock options 7,425,444 ​ 6,199,571 Shares reserved for vesting of outstanding restricted stock units 1,370,897 ​ 1,112,563 Shares reserved for issuances under the 2015 Stock Option Plan ​ 3,572,195 ​ 3,536,932 ​ Shares reserved for issuances under the 2015 Employee Stock Purchase Plan ​ 2,158,966 ​ 1,884,309 ​ ​ 14,550,002 ​ 12,778,375 ​

Stock-based compensation (Table

Stock-based compensation (Tables)	12 Months Ended
	Dec. 31, 2023
Stock-based compensation
Compensation cost recognized for all stock-based compensation awards	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year ended December 31, ​ 2023 2022 2021 ​ ​ (in thousands) General and administrative ​ $ 7,568 ​ $ 6,398 ​ $ 7,191 ​ Research and development ​ 3,585 ​ 2,946 ​ 4,133 ​ Total stock-based compensation expense ​ $ 11,153 ​ $ 9,344 ​ $ 11,324 ​
Summary of stock-based compensation expense by type of award	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year ended December 31, ​ ​ ​ 2023 2022 2021 ​ ​ ​ (in thousands) ​ Stock options ​ $ 7,627 ​ $ 5,938 ​ $ 7,438 ​ Restricted stock awards and units ​ ​ 3,241 ​ ​ 3,215 ​ ​ 3,551 ​ Employee stock purchase plan awards ​ 285 ​ 191 ​ 335 ​ Total stock-based compensation expense ​ $ 11,153 ​ $ 9,344 ​ $ 11,324 ​
Summary of status and changes in unvested restricted stock	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted ​ ​ ​ ​ ​ Average ​ ​ ​ ​ ​ Grant Date ​ ​ ​ ​ ​ Fair Value ​ ​ ​ Units Per Unit ​ Unvested restricted stock units as of December 31, 2022 ​ 1,112,563 ​ $ 5.27 ​ Awarded ​ 999,250 ​ $ 7.58 ​ Vested ​ (531,560) ​ $ 5.73 ​ Forfeited ​ (209,356) ​ $ 6.08 ​ Unvested restricted stock units as of December 31, 2023 ​ 1,370,897 ​ $ 6.65 ​
Summary of stock option activity	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted Remaining Aggregate ​ ​ ​ ​ ​ Average ​ Contractual ​ Intrinsic ​ ​ ​ ​ ​ Exercise ​ Life ​ Value ​ ​ ​ Shares Price (in years) (in thousands) ​ Outstanding at December 31, 2022 ​ 6,199,571 ​ $ 8.12 ​ ​ ​ ​ ​ Granted ​ 2,326,800 ​ $ 8.58 ​ ​ ​ ​ ​ ​ Exercised ​ (385,655) ​ $ 4.98 ​ ​ ​ ​ ​ ​ Cancelled or forfeited ​ (715,272) ​ $ 7.86 ​ ​ ​ ​ ​ ​ Outstanding at December 31, 2023 ​ 7,425,444 ​ $ 8.52 ​ 7.3 ​ ​ 11,293 ​ Exercisable at December 31, 2023 ​ 3,823,420 ​ $ 9.43 5.9 ​ $ 6,020 ​
Summary of weighted-average assumptions	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year ended December 31, ​ ​ 2023 2022 2021 ​ Risk-free interest rate 4.0 % 2.2 % 0.9 % ​ Expected dividend yield — % — % — % ​ Expected term (in years) 6.0 ​ 6.0 ​ 6.0 ​ ​ Expected volatility 80.4 % 79.4 % 75.0 % ​

Income taxes (Tables)

Income taxes (Tables)	12 Months Ended
	Dec. 31, 2023
Income taxes
Schedule of components of income expense (benefit)	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year ended December 31, ​ 2023 ​ 2022 ​ 2021 ​ (in thousands) ​ ​ ​ Current ​ ​ ​ ​ ​ ​ ​ ​ Federal $ 1,248 ​ $ — ​ $ — State ​ 160 ​ ​ 16 ​ ​ — Total current ​ 1,408 ​ ​ 16 ​ ​ — ​ ​ ​ ​ ​ ​ ​ ​ ​ Deferred ​ ​ ​ ​ ​ ​ ​ ​ Federal ​ — ​ ​ — ​ ​ — State ​ — ​ ​ — ​ ​ — Total deferred ​ — ​ ​ — ​ ​ — Total tax provision $ 1,408 ​ $ 16 ​ $ —
Schedule of reconciliation of the expected income tax (benefit) computed using the federal statutory income tax rate to the effective income tax rate	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year ended December 31, ​ ​ 2023 ​ 2022 ​ 2021 ​ Income tax computed at federal statutory tax rate ​ 21.0 % ​ 21.0 % ​ 21.0 % ​ State taxes, net of federal benefit ​ 5.4 % ​ 5.2 % ​ 6.6 % ​ Provision to return ​ 0.9 % ​ 3.2 % ​ 4.9 % ​ General business credit carryovers ​ (0.4) % ​ (3.5) % ​ 3.2 % ​ Non-deductible expenses ​ 0.5 % ​ (4.6) % ​ (3.8) % ​ Other ​ (0.4) % ​ — % ​ — % ​ Change in valuation allowance ​ (26.0) % ​ (21.3) % ​ (31.9) % ​ Total ​ 1.00 % ​ — % ​ — % ​
Schedule of principal components of the Company's deferred tax assets and liabilities	​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, ​ ​ 2023 ​ 2022 ​ (in thousands) ​ Deferred tax assets: ​ ​ ​ ​ ​ ​ Net operating loss carryforward $ 13,724 ​ $ 47,282 ​ Tax credit carryforward 28,427 ​ 32,060 ​ Lease liability ​ 5,544 ​ ​ 6,318 ​ Deferred revenue ​ 1,675 ​ ​ 17,984 ​ Stock compensation ​ 5,157 ​ ​ 4,630 ​ Non-deductible accruals and reserves 2,613 ​ 1,603 ​ Capitalized research expenses ​ 31,347 ​ ​ 14,351 ​ Intangibles 554 ​ 610 ​ Other temporary differences ​ — ​ ​ (1) ​ Total deferred tax assets 89,041 ​ 124,837 ​ Less valuation allowance (82,612) ​ (117,416) ​ Net deferred tax assets 6,429 ​ 7,421 ​ Deferred tax liabilities ​ ​ ​ ​ ​ Right of use assets ​ (3,691) ​ (4,231) ​ Depreciation and amortization ​ (2,738) ​ ​ (3,190) ​ Other temporary differences ​ — ​ ​ — ​ Net deferred taxes $ — ​ $ — ​

Nature of business (Details)

Nature of business (Details) - USD ($) $ in Thousands					1 Months Ended	12 Months Ended
	Jan. 04, 2024	Dec. 28, 2023	Mar. 04, 2022	Oct. 01, 2021	Jan. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Accumulated deficit						$ (261,182)	$ (393,512)
Cash, cash equivalents, and marketable debt securities						230,900
Subsequent Event. | Over-Allotment Option
Net proceeds received	$ 93,500
Pfizer | Option and license agreement
Upfront payment				$ 30,000
Novartis Pharma, AG | Option and license agreement
Upfront payment			$ 54,000
Novartis Pharma, AG | 2023 Novartis Collaboration Agreement
Upfront payment						$ 80,000
Proceeds from issuance of common stock		$ 20,000
Novartis Pharma, AG | Forecast | Novartis License and Collaboration Agreement
Upfront payment					$ 80,000

Summary of significant accoun_4

Summary of significant accounting policies and basis of presentation - Cash, Cash Equivalents, and Marketable Securities - (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Amortized Cost Basis [Abstract]
Cash and cash equivalents	$ 68,802	$ 98,959	$ 117,433
Total money market funds and marketable securities	227,583	111,704
Fair Value Disclosure [Abstract]
Total money market funds and marketable securities	227,663	111,613
Unrealized Gain and Loss [Abstract]
Marketable securities, unrealized gains	93
Marketable securities, unrealized losses	(13)	(91)
Debt securities, unrealized loss position	44,200	19,900
Other than temporary losses	0
Money market funds
Amortized Cost Basis [Abstract]
Cash and cash equivalents	65,589	91,724
Fair Value Disclosure [Abstract]
Cash and cash equivalents	65,589	91,724
U.S. Treasury notes
Amortized Cost Basis [Abstract]
Marketable securities, amortized cost	102,966	19,980
Fair Value Disclosure [Abstract]
Marketable securities, fair value	103,044	19,889
Unrealized Gain and Loss [Abstract]
Marketable securities, unrealized gains	81
Marketable securities, unrealized losses	(3)	$ (91)
U. S. Government agency securities
Amortized Cost Basis [Abstract]
Marketable securities, amortized cost	31,068
Fair Value Disclosure [Abstract]
Marketable securities, fair value	31,075
Unrealized Gain and Loss [Abstract]
Marketable securities, unrealized gains	10
Marketable securities, unrealized losses	(3)
Corporate bonds
Amortized Cost Basis [Abstract]
Marketable securities, amortized cost	23,975
Fair Value Disclosure [Abstract]
Marketable securities, fair value	23,970
Unrealized Gain and Loss [Abstract]
Marketable securities, unrealized gains	2
Marketable securities, unrealized losses	(7)
Commercial paper
Amortized Cost Basis [Abstract]
Marketable securities, amortized cost	3,985
Fair Value Disclosure [Abstract]
Marketable securities, fair value	$ 3,985
Maximum
Unrealized Gain and Loss [Abstract]
Debt securities, contractual maturity period	1 year	1 year

Summary of significant accoun_5

Summary of significant accounting policies and basis of presentation - Restricted Cash - (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Summary of significant accounting policies and basis of presentation
Cash and cash equivalents	$ 68,802	$ 98,959	$ 117,433
Restricted cash included in deposits and other noncurrent assets	1,593	1,515	1,779
Total cash, cash equivalents, and restricted cash	$ 70,395	$ 100,474	$ 119,212	$ 106,219

Summary of significant accoun_6

Summary of significant accounting policies and basis of presentation - Stock Based Compensation Expense - (Details)	12 Months Ended
	Dec. 31, 2023
Summary of significant accounting policies and basis of presentation
Expected dividend yield	0%

Summary of significant accoun_7

Summary of significant accounting policies and basis of presentation - Net income (loss) per share - (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities	8,818,841	7,357,134	5,956,827
Numerator:
Net income (loss)	$ 132,330	$ (46,408)	$ (71,197)
Denominator for basic net income (loss) per share:
Weighted average shares outstanding-basic	43,020,747	38,356,810	37,668,947
Denominator for diluted net income (loss) per share:
Weighted average shares outstanding-basic	43,020,747	38,356,810	37,668,947
Common stock options and restricted stock units	1,548,587
Weighted average shares outstanding-diluted	44,569,334	38,356,810	37,668,947
Financial instruments with off-balance sheet risk	$ 0
Unvested restricted common stock awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities	22,500	45,000	137,255
Unvested restricted common stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities	1,370,897	1,112,563	806,379
Employee Stock Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities	7,425,444	6,199,571	5,013,193

Fair value measurements - Asset

Fair value measurements - Assets and liabilities measured on a recurring basis - (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	$ 68,802	$ 98,959	$ 117,433
Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Total assets measured at fair value	227,663	111,613
Level 1 | Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Total assets measured at fair value	199,708	111,613
Level 2 | Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Total assets measured at fair value	27,955
U.S. Treasury notes | Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Marketable securities	103,044	19,889
U.S. Treasury notes | Level 1 | Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Marketable securities	103,044	19,889
U. S. Government agency securities | Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Marketable securities	31,075
U. S. Government agency securities | Level 1 | Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Marketable securities	31,075
Corporate bonds | Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Marketable securities	23,970
Corporate bonds | Level 2 | Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Marketable securities	23,970
Commercial paper | Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Marketable securities	3,985
Commercial paper | Level 2 | Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Marketable securities	3,985
Money market funds
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	65,589	91,724
Money market funds | Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	65,589	91,724
Money market funds | Level 1 | Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents	$ 65,589	$ 91,724

Prepaid expenses and other cu_3

Prepaid expenses and other current assets (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Prepaid expense and other current assets
Other current assets	$ 2,628	$ 4,233
Prepaid insurance	607	696
Prepaid research and development contracts	1,119	83
Accrued interest receivable	964	382
Total	$ 5,318	$ 5,394

Property and equipment, net (De

Property and equipment, net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 31,532	$ 35,064
Less: accumulated depreciation	(15,038)	(17,207)
Property and equipment, net	16,494	17,857
Depreciation expense	4,441	6,191	$ 5,165
Laboratory equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	20,536	19,675
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	7,106	12,554
Furniture and office equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	2,625	2,333
Other
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 1,265	$ 502

Accrued expenses (Details)

Accrued expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Accrued expenses
Employee compensation costs	$ 6,614	$ 4,559
Research and development costs	5,225	1,895
Accrued goods and services	4,229	636
Professional services	755	726
Total	$ 16,823	$ 7,816

Lease obligation (Details)

Lease obligation (Details) $ in Thousands		3 Months Ended	12 Months Ended
	Jun. 22, 2022 USD ($)	Jun. 30, 2022 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Feb. 01, 2024 USD ($)	Aug. 11, 2023 ft²	Sep. 30, 2021
Change in operating lease, right-of-use assets			$ (1,975)	$ (3,462)	$ (2,606)
Change in operating lease liabilities			(2,833)	(3,922)	(3,428)
Gain on lease termination				2,468
Restricted cash included in deposits and other noncurrent assets			1,593	1,515	1,779
Lease expense			$ 3,600	$ 4,600	$ 6,800
Weighted average remaining lease term			5 years
Weighted average incremental borrowing rate			7.40%
Total minimum lease payments
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]			Other Liabilities, Current	Other Liabilities, Current
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]			Other Liabilities, Noncurrent	Other Liabilities, Noncurrent
75 Sidney Street
Sublease term								3 years 3 months 18 days
Change in operating lease, right-of-use assets	$ (14,500)
Change in operating lease liabilities		$ (17,000)
Gain on lease termination		$ 2,500
Restricted cash included in deposits and other noncurrent assets			$ 1,500
75 Hayden Avenue
Lease term						7 years
Expected contractual obligation for lease not yet commenced						$ 37,800
Area of additional facility leased | ft²							61,307

Lease obligation - Operating su

Lease obligation - Operating sublease income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Lease obligation
Operating sublease income		$ 1,380	$ 838
Operating Lease, Lease Income, Statement of Income or Comprehensive Income [Extensible Enumeration]	Operating Expenses	Operating Expenses	Operating Expenses

Commitments, contingencies, a_3

Commitments, contingencies, and other liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2023	Dec. 31, 2022
Other current liabilities
Lease liability		$ 3,200	$ 2,832
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]		Total other current liabilities	Total other current liabilities
Total other current liabilities		$ 3,200	$ 2,832
Other non-current liabilities
Lease liability		$ 17,093	$ 20,294
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]		Total other non-current liabilities	Total other non-current liabilities
Other		$ 1,001	$ 1,001
Total other non-current liabilities		$ 18,094	$ 21,295
Restructuring costs	$ 2,600

Significant Agreements - Novart

Significant Agreements - Novartis Agreements (Details) $ in Thousands		1 Months Ended	12 Months Ended
	Mar. 04, 2022 USD ($) item	Jan. 31, 2024 USD ($)	Dec. 31, 2023 USD ($) item	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 28, 2023 USD ($) shares
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Purchase of common stock			$ 31,121
Collaboration revenue			250,008	$ 40,907	$ 37,415
Related party collaboration receivable			3,341	$ 257
Novartis Pharma, AG | 2023 Novartis Collaboration Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Upfront payment			80,000
Shares of common stock | shares						2,145,002
Aggregate purchase price						$ 20,000
Allocation of fixed consideration			$ 80,000
Number of days written notice required by reporting entity to terminate agreement			90 days
Costs to obtain collaboration agreement			$ 1,900
Revenue recognized			80,000
Related party collaboration receivable			80,000
Contract expense			1,900
Novartis Pharma, AG | Option and license agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of transgenes | item	3
Number of additional targets | item	2
Upfront payment	$ 54,000
Number of license options | item	3
Number of license options on additional targets | item	5
Number of license option exercise for each target | item	1
Number of alliance managers | item	2
Number of options | item	1
Number of major market countries received regulatory approval | item	3
Number of days written notice required by reporting entity to terminate agreement	90 days
Number of performance obligations | item	3
Number of material rights | item	3
Allocation of transaction price	$ 18,000		25,000
Revenue recognized			79,000
Collaboration revenue			79,000
Novartis Pharma, AG | Option and license agreement | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of license options | item	1
Novartis Pharma, AG | First and Second Material Right
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Allocation of transaction price			54,000
Novartis Pharma, AG | Subsequent events | 2023 Novartis Collaboration Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Amount of premium		$ 700
Novartis Pharma, AG | Sales milestone | 2023 Novartis Collaboration Agreement | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Allocation of variable consideration			775,000
Novartis Pharma, AG | Development milestone | 2023 Novartis Collaboration Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Allocation of variable consideration			425,000
Novartis Pharma, AG | SMA Program | Development, regulatory and commercialization milestone | 2023 Novartis Collaboration Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Aggregate maximum milestone payments to be received from collaborative partner			200,000
Novartis Pharma, AG | SMA Program | Sales milestone | 2023 Novartis Collaboration Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Aggregate maximum milestone payments to be received from collaborative partner			400,000
Novartis Pharma, AG | HD Program | 2023 Novartis Collaboration Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Allocation of variable consideration			24,200
Novartis Pharma, AG | HD Program | Development, regulatory and commercialization milestone | 2023 Novartis Collaboration Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Aggregate maximum milestone payments to be received from collaborative partner			225,000
Novartis Pharma, AG | HD Program | Sales milestone | 2023 Novartis Collaboration Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Aggregate maximum milestone payments to be received from collaborative partner			$ 375,000
Novartis Pharma, AG | Discovery Programs 2023 | 2023 Novartis Collaboration Agreement | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of options | item			4

Significant Agreements - Neuroc

Significant Agreements - Neurocrine Collaboration Agreements (Details) $ / shares in Units, $ in Thousands		1 Months Ended			3 Months Ended				12 Months Ended
	Jan. 08, 2023 USD ($) $ / shares shares	Feb. 28, 2023 USD ($) item Program $ / shares shares	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($) Program item $ / shares shares	Dec. 31, 2023 USD ($) item	Mar. 31, 2023 item	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2023 USD ($) item shares	Dec. 31, 2022 USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Purchase of common stock									$ 31,121
Allocation of Transaction Price
Deferred revenue, current					$ 42,881		$ 59,377		42,881	$ 59,377
Deferred revenue, non-current					32,359		6,450		32,359	6,450
Related party collaboration receivable					3,341		257		$ 3,341	257
Neurocrine Collaborative Agreement 2019 | FA Program
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Percentage of profit or loss under co-co option				40%
Neurocrine Collaborative Agreement 2019 | Neurocrine
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of discovery programs				2					92,382
Programs added later | item				2
Discovery programs under development | item				2
Number of targets | item				8
Upfront payment				$ 115,000					$ 115,000
Purchase of common stock, shares | shares				4,179,728					4,179,728
Purchase of common stock				$ 50,000					$ 5,000
Price per share | $ / shares				$ 11.9625
Aggregate maximum milestone payments to be received from collaborative partner				$ 170,000
Estimated cost reimbursement					83,300		$ 81,700	$ 80,000	431,100
Termination period				10 years
Period of advance notice for termination prior to first commercial sale				180 days
Period of advance notice for termination after first commercial sale				1 year
Discount related to equity investment									27,600
Equity investment					50,000				50,000
Allocation of Transaction Price
Allocation of variable consideration					83,251				83,251
Allocation of fixed consideration					92,400				92,400
Cumulative catch up of revenue recognized									900
Reimbursement costs expected to be received									1,600
Costs to obtain collaboration agreement					800				800
Consideration received			$ 5,000
Deferred revenue					6,100				6,100
Neurocrine Collaborative Agreement 2019 | Neurocrine | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Percentage of reduction in royalty payments				50%
Neurocrine Collaborative Agreement 2019 | Neurocrine | VY-AADC
Allocation of Transaction Price
Allocation of variable consideration					53,863				53,863
Allocation of fixed consideration					49,045				49,045
Neurocrine Collaborative Agreement 2019 | Neurocrine | FA Program
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Percentage of profit or loss under co-co option				60%
Allocation of Transaction Price
Allocation of variable consideration					20,309				20,309
Allocation of fixed consideration					20,647				20,647
Neurocrine Collaborative Agreement 2019 | Neurocrine | Discovery and FA Programs
Allocation of Transaction Price
Allocation of fixed consideration					42,200				42,200
Neurocrine Collaborative Agreement 2019 | Neurocrine | Discovery program 1
Allocation of Transaction Price
Allocation of variable consideration					4,286				4,286
Allocation of fixed consideration					14,443				14,443
Neurocrine Collaborative Agreement 2019 | Neurocrine | Discovery program 2
Allocation of Transaction Price
Allocation of variable consideration					4,793				4,793
Allocation of fixed consideration					$ 8,247				8,247
Neurocrine Collaborative Agreement 2019 | Neurocrine | Active programs
Allocation of Transaction Price
Revenue recognized									$ 9,800	$ 900
Neurocrine Collaborative Agreement 2019 | Neurocrine | Development and regulatory milestones | FA Program
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Aggregate maximum milestone payments to be received from collaborative partner				$ 195,000
Neurocrine Collaborative Agreement 2019 | Neurocrine | Development and regulatory milestones | Discovery program 1
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Aggregate maximum milestone payments to be received from collaborative partner				130,000
Neurocrine Collaborative Agreement 2019 | Neurocrine | Commercial milestone
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Per milestone, maximum milestone payments to be received from collaborative partner				275,000
Aggregate maximum milestone payments to be received from collaborative partner				$ 1,100,000
Neurocrine Collaborative Agreement 2023
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Percentage of profit or loss under co-co option	50%
Percentage of development costs incurred	50%
Neurocrine Collaborative Agreement 2023 | Development milestone | Minimum
Allocation of Transaction Price
Number of countries received regulatory approval | item					1				1
Neurocrine Collaborative Agreement 2023 | Neurocrine
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of collaboration programs | item									3
Number of discovery programs | item						3			3
Number of development and commercialization licenses | item									2
Percentage of profit or loss under co-co option	50%
Percentage of development costs incurred	50%
Upfront payment		$ 136,000
Purchase of common stock, shares | shares	4,395,588	4,395,588
Purchase of common stock	$ 39,000	$ 39,000
Price per share | $ / shares	$ 8.88	$ 8.88
Termination period		10 years
Amount of premium		$ 7,900
Period of advance notice for termination prior to first commercial sale		180 days
Period of advance notice for termination after first commercial sale		1 year
Period of advance notice for termination after complete readout of clinical trial		30 days
Discount related to equity investment		$ 39,000
Allocation of Transaction Price
Allocation of variable consideration					$ 11,259				$ 11,259
Allocation of fixed consideration		$ 143,900			143,880				143,880
Cumulative catch up of revenue recognized									69,100
Reimbursement costs expected to be received									11,300
Costs to obtain collaboration agreement					400				400
Deferred revenue, current					38,400				38,400
Deferred revenue, non-current					30,700				30,700
Related party collaboration receivable					1,800				1,800
Neurocrine Collaborative Agreement 2023 | Neurocrine | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Percentage of reduction in royalty payments		50%
Neurocrine Collaborative Agreement 2023 | Neurocrine | GBA1
Allocation of Transaction Price
Allocation of variable consideration					5,920				5,920
Allocation of fixed consideration					69,459				69,459
Revenue recognized									69,500
Neurocrine Collaborative Agreement 2023 | Neurocrine | Discovery program 1
Allocation of Transaction Price
Allocation of variable consideration					3,779				3,779
Allocation of fixed consideration					24,807				24,807
Neurocrine Collaborative Agreement 2023 | Neurocrine | Discovery program 2
Allocation of Transaction Price
Allocation of variable consideration					780				780
Allocation of fixed consideration					24,807				24,807
Neurocrine Collaborative Agreement 2023 | Neurocrine | Discovery program 3
Allocation of Transaction Price
Allocation of variable consideration					780				780
Allocation of fixed consideration					$ 24,807				$ 24,807
Neurocrine Collaborative Agreement 2023 | Neurocrine | Discovery Programs 2023
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of discovery programs | item									3
Allocation of Transaction Price
Revenue recognized									$ 5,500
Neurocrine Collaborative Agreement 2023 | Neurocrine | Development milestone
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Discovery programs under development | Program		3
Neurocrine Collaborative Agreement 2023 | Neurocrine | Development milestone | GBA1
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Aggregate maximum milestone payments to be received from collaborative partner		$ 985,000
Neurocrine Collaborative Agreement 2023 | Neurocrine | Development milestone | Discovery Programs 2023
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Aggregate maximum milestone payments to be received from collaborative partner		175,000
Neurocrine Collaborative Agreement 2023 | Neurocrine | Commercial milestone | GBA1 | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Per milestone, maximum milestone payments to be received from collaborative partner		$ 950,000
Allocation of Transaction Price
Number of products | item		2
Neurocrine Collaborative Agreement 2023 | Neurocrine | Commercial milestone | Discovery Programs 2023
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Per milestone, maximum milestone payments to be received from collaborative partner		$ 275,000
Allocation of Transaction Price
Number of products | item		1
Neurocrine Collaborative Agreement 2023 | Neurocrine | Research and development milestone | GBA1
Allocation of Transaction Price
Revenue recognized									$ 5,800

Significant Agreements - Neur_2

Significant Agreements - Neurocrine Collaboration receivables and contract liabilities (Details) $ in Thousands	1 Months Ended	3 Months Ended	12 Months Ended
	Mar. 31, 2019 Program	Mar. 31, 2023 USD ($) item	Dec. 31, 2023 USD ($) item
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Related party collaboration receivables, beginning balance		$ 257	$ 257
Related party collaboration receivables, ending balance			3,341
Neurocrine collaborative Agreement 2023 and Neurocrine Collaborative Agreement 2019
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Related party collaboration receivables, beginning balance		257	257
Additions			10,081
Deductions			(6,997)
Related party collaboration receivables, ending balance			3,341
Deferred revenue, beginning balance		$ 11,827	11,827
Additions			74,420
Deductions			(11,007)
Deferred revenue, ending balance			75,240
Neurocrine | Neurocrine Collaborative Agreement 2023
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Related party collaboration receivables, ending balance			$ 1,800
Number of discovery programs | item		3	3
Neurocrine | Neurocrine Collaborative Agreement 2019
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Deferred revenue, ending balance			$ 6,100
Number of discovery programs	2		92,382
Discovery program 3 | Neurocrine | Neurocrine collaborative Agreement 2023 and Neurocrine Collaborative Agreement 2019
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Additions		$ 74,400
Deductions			$ 11,000

Significant Agreements - Alexio

Significant Agreements - Alexion Option and License Agreement (Details) $ in Thousands		12 Months Ended
	Oct. 01, 2021 USD ($) item	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration revenue		$ 250,008	$ 40,907	$ 37,415
Pfizer | Option and license agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of transgenes | item	2
Number of options | item	1
Number of performance obligations | item	2
Number of material rights | item	2
Upfront payment	$ 30,000
Non-refundable upfront payment received	$ 30,000
Number of license options | item	1
Allocation of transaction price	$ 15,000
Aggregate milestone payments, if exercise rights	$ 10,000
Revenue recognized		$ 0	$ 40,000
Pfizer | Second Material Right
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of days written notice required by reporting entity to terminate agreement	90 days
Pfizer | Development, regulatory and commercialization milestone | Option and license agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Aggregate maximum milestone payments to be received from collaborative partner	$ 115,000
Pfizer | Sales milestone | Option and license agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Aggregate maximum milestone payments to be received from collaborative partner	$ 175,000
Minimum | Pfizer | Option and license agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of countries received regulatory approval | item	1
Number of major market countries received regulatory approval | item	1

Significant Agreements - Sangam

Significant Agreements - Sangamo (Details) $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($)
License Agreement | Sangamo
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue recognized	$ 0.4

Significant Agreements - Touchl

Significant Agreements - Touchlight IP Ltd License Agreement (Details) - Touchlight IP Ltd License Agreement - Touchlight IP Ltd - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2023
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Non-refundable technology access fee payable	$ 5	$ 0.5
Non-refundable technology access fee	$ 5

Significant Agreements - Litiga

Significant Agreements - Litigation (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Loss Contingency [Abstract]
Contingency reserves for litigation liabilities	$ 0	$ 0

Common stock (Details)

Common stock (Details) - $ / shares	Dec. 31, 2023	Dec. 31, 2022	Oct. 31, 2015
Class of Stock [Line Items]
Common Stock, Shares Authorized	120,000,000	120,000,000
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Shares available for future issuance (in shares)	14,550,002	12,778,375
2015 Stock Option Plan
Class of Stock [Line Items]
Shares available for future issuance (in shares)	3,572,195	3,536,932	1,311,812
2015 Employee Stock Purchase Plan.
Class of Stock [Line Items]
Shares available for future issuance (in shares)	2,158,966	1,884,309
Employee Stock Option [Member]
Class of Stock [Line Items]
Shares available for future issuance (in shares)	7,425,444	6,199,571
Unvested restricted common stock units
Class of Stock [Line Items]
Shares available for future issuance (in shares)	1,370,897	1,112,563
Founders restricted stock
Class of Stock [Line Items]
Shares available for future issuance (in shares)	22,500	45,000

Stock-based compensation (Detai

Stock-based compensation (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		12 Months Ended			96 Months Ended
	Oct. 31, 2015	Jan. 31, 2014	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2023
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future issuance (in shares)			14,550,002	12,778,375		14,550,002
Stock options granted (in shares)			2,326,800
Stock-based compensation.			$ 11,153	$ 9,344	$ 11,324
2014 Stock Option and Grant Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized for stock-based compensation plan (in shares)		823,529
2015 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future issuance (in shares)				2,158,966
Percentage of outstanding common stock						1%
Common stock shares authorized for issuance						2,692,838
New stock options issued			111,639	150,265
Number of shares authorized for stock-based compensation plan (in shares)	262,362
Period to purchase shares			6 months
2015 Employee Stock Purchase Plan | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of payroll deduction	1%
2015 Employee Stock Purchase Plan | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of payroll deduction	10%
2015 Stock Option Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future issuance (in shares)	1,311,812		3,572,195	3,536,932		3,572,195
Percentage limit of issued and outstanding shares up to which additional shares may be issued	4%
Percentage of outstanding common stock						4%
Common stock shares authorized for issuance						12,531,505
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future issuance (in shares)			7,425,444	6,199,571		7,425,444
Stock-based compensation.			$ 7,627	$ 5,938	7,438
Employee Stock Option [Member] | Inducement Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			4 years
Employee Stock Option [Member] | Inducement Awards | Vesting period, tranche one
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage			25%
Employee Stock Option [Member] | Inducement Awards | Vesting period, tranche two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			36 months
Vesting percentage			75%
Unvested restricted common stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future issuance (in shares)			1,370,897	1,112,563		1,370,897
Stock-based compensation.			$ 3,241	$ 3,215	$ 3,551
Vesting period			3 years
Restricted stock granted, original issued price (in dollars per share)			$ 7.58
Granted (in shares)			999,250
Unvested restricted common stock units | Inducement Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
New stock options issued			318,500	163,000	13,000
Vesting period			3 years
Unvested restricted common stock units | Inducement Awards | Vesting period, tranche one
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage			33%
Unvested restricted common stock units | Inducement Awards | Vesting period, tranche two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage			33%
Performance based milestone awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Remaining number of shares authorized to be repurchased			131,470			131,470
Founders restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future issuance (in shares)			22,500	45,000		22,500
Restricted stock granted (in shares)		1,188,233
Restricted stock granted, original issued price (in dollars per share)		$ 0.0425
Founders restricted stock | Vesting period, tranche one
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock granted (in shares)		835,292
Founders restricted stock | Minimum | Vesting period, tranche one
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		1 year
Founders restricted stock | Maximum | Vesting period, tranche one
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		4 years
Non-statutory stock options | Inducement Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
New stock options issued			573,000	390,000	76,500
Employees and directors stock options | 2014 Stock Option and Grant Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			4 years
Employees and directors stock options | 2014 Stock Option and Grant Plan | Vesting period, tranche one
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			1 year
Vesting percentage			25%
Employees and directors stock options | 2014 Stock Option and Grant Plan | Vesting period, tranche two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			3 years
Vesting percentage			75%
Employees and directors stock options | 2015 Stock Option Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted (in shares)			1,753,800
Non-employees stock options | 2014 Stock Option and Grant Plan | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			1 year
Non-employees stock options | 2014 Stock Option and Grant Plan | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			4 years
Share-based Payment Arrangement, Employee | Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation.			$ 7,200	$ 5,800	$ 7,300
Share-based Payment Arrangement, Employee | Unvested restricted common stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation.			3,100	2,900	3,300
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation.			3,585	2,946	4,133
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation.			$ 7,568	$ 6,398	$ 7,191

Stock-based compensation - Comp

Stock-based compensation - Compensation expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 11,153	$ 9,344	$ 11,324
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	7,627	5,938	7,438
Restricted stock awards and units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	3,241	3,215	3,551
Employee stock purchase plan awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	285	191	335
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	3,585	2,946	4,133
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 7,568	$ 6,398	$ 7,191

Stock-based compensation - Rest

Stock-based compensation - Restricted Stock - (Details) - Unvested restricted common stock units $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($) $ / shares shares
Shares
Balance, beginning (in shares) | shares	1,112,563
Granted (in shares) | shares	999,250
Vested (in shares) | shares	(531,560)
Forfeited (in shares) | shares	(209,356)
Balance, ending (in shares) | shares	1,370,897
Weighted Average Grant Date Fair Value Per Share
Balance, beginning (in dollars per share) | $ / shares	$ 5.27
Granted (in dollars per share) | $ / shares	7.58
Vested (in dollars per share) | $ / shares	5.73
Forfeited (in dollars per share) | $ / shares	6.08
Balance, ending (in dollars per share) | $ / shares	$ 6.65
Restricted stock disclosures
Vesting period	3 years
Unrecognized stock-based compensation expense | $	$ 6.8
Remaining weighted-average remaining vesting period	1 year 1 month 6 days

Stock-based compensation - Stoc

Stock-based compensation - Stock Options - (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding, beginning balance (in shares) | shares	6,199,571
Granted (in shares) | shares	2,326,800
Exercised (in shares) | shares	(385,655)
Cancelled or forfeited (in shares) | shares	(715,272)
Outstanding, ending balance (in shares) | shares	7,425,444
Exercisable (in shares) | shares	3,823,420
Weighted Average Exercise Price
Outstanding (in dollars per share)	$ 8.12
Granted (in dollars per share)	8.58
Exercised (in dollars per share)	4.98
Cancelled or forfeited (in dollars per share)	7.86
Outstanding (in dollars per share)	8.52
Exercisable (in dollars per share)	$ 9.43
Remaining Contractual Life
Outstanding	7 years 3 months 18 days
Exercisable	5 years 10 months 24 days
Aggregate Intrinsic Value
Outstanding | $	$ 11,293
Exercisable | $	$ 6,020
Employee Stock Option [Member]
Options disclosures
Weighted average fair value of grants (in dollars per share)	$ 6.12
Unrecognized stock-based compensation expense | $	$ 16,600
Remaining weighted-average remaining vesting period	2 years 10 months 24 days

Stock-based compensation - Unre

Stock-based compensation - Unrecognized expense and weighted-average period (Details) - $ / shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Fair value assumptions
Expected dividend yield	0%
Employee Stock Option [Member]
Options disclosures
Weighted average fair value of grants (in dollars per share)	$ 6.12
Remaining weighted-average remaining vesting period	2 years 10 months 24 days
Employees and directors stock options
Fair value assumptions
Risk-free interest rate	4%	2.20%	0.90%
Expected term	6 years	6 years	6 years
Expected volatility	80.40%	79.40%	75%

401(k) Savings plan (Details)

401(k) Savings plan (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
401(k) Savings plan
Employer contribution expense	$ 1.1	$ 0.9	$ 1.1

Income taxes (Details)

Income taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Current
Federal	$ 1,248
State	160	$ 16
Total current	1,408	16
Total tax provision	$ 1,408	$ 16

Income taxes - Net operating lo

Income taxes - Net operating loss carryforwards (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Operating Loss Carryforwards [Line Items]
Valuation Allowance	$ 82,612	$ 117,416
Change in the valuation allowance	$ (34,800)
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Income tax computed at federal statutory tax rate	21%	21%	21%
State taxes, net of federal benefit	5.40%	5.20%	6.60%
Provision to return	0.90%	3.20%	4.90%
General business credit carryovers	(0.40%)	(3.50%)	3.20%
Nondeductible expenses	0.50%	(4.60%)	(3.80%)
Other	(0.40%)
Change in valuation allowance	(26.00%)	(21.30%)	(31.90%)
Total	1%
Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 55,300
State
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	33,200
Investment tax credit		$ 400
Research and development tax credits carryforwards | Federal
Operating Loss Carryforwards [Line Items]
Tax credits carryforwards	19,600
Research and development tax credits carryforwards | State
Operating Loss Carryforwards [Line Items]
Tax credits carryforwards	$ 10,800

Income taxes - Deferred tax ass

Income taxes - Deferred tax assets (liabilities) and unrecognized tax benefits (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Income taxes
Unrecognized tax benefits	$ 0	$ 0
Amounts in uncertain tax position	0
Accrued interest	0	0
Deferred tax assets:
Net operating loss carryforwards	13,724	47,282
Tax credit carryforwards	28,427	32,060
Lease liability	5,544	6,318
Deferred revenue	1,675	17,984
Stock compensation	5,157	4,630
Non-deductible accruals and reserves	2,613	1,603
Capitalized research expenses	31,347	14,351
Intangibles	554	610
Other temporary differences		(1)
Total deferred tax assets	89,041	124,837
Less valuation allowance	(82,612)	(117,416)
Net deferred tax assets	6,429	7,421
Deferred tax liabilities
Right of use assets	(3,691)	(4,231)
Depreciation and amortization	$ (2,738)	$ (3,190)

Related party transactions (Det

Related party transactions (Details)	12 Months Ended
	Dec. 31, 2023 USD ($) item	Dec. 31, 2022 USD ($) item	Dec. 31, 2021 USD ($) item
Related party transactions
Related party collaboration receivable	$ 3,341,000	$ 257,000
Former Executives | Related Party | Board and scientific advisory services
Related party transactions
Number of individuals providing services | item	1	1	1
Dr. Sah | Related Party | Board and scientific advisory services
Related party transactions
Total amount of services received	$ 700,000	$ 500,000	$ 200,000
Dr. Sandrock | Related Party | Consulting and advisor services
Related party transactions
Total amount of services received		$ 60,000
Neurocrine | Related Party | Collaboration arrangement
Related party transactions
Related party collaboration receivable	$ 3,300,000

Subsequent events (Details)

Subsequent events (Details) - USD ($) $ / shares in Units, $ in Thousands			12 Months Ended
	Feb. 02, 2024	Jan. 04, 2024	Dec. 31, 2023	Mar. 31, 2024	Feb. 29, 2024	Dec. 28, 2023	Dec. 31, 2022
Subsequent events
Par value of common stock (in dollars per share)			$ 0.001				$ 0.001
Purchase of common stock			$ 31,121
2023 Novartis Collaboration Agreement | Novartis
Subsequent events
Shares of common stock						2,145,002
Number of shares agreed to be issued, price per share						$ 9.324
Aggregate purchase price						$ 20,000
Subsequent events
Subsequent events
Offering price for common stock		$ 9
Subsequent events | Neurocrine
Subsequent events
Milestone payment to be received				$ 5,000	$ 5,000
Subsequent events | Pre-Funded Warrants
Subsequent events
Offering price for warrants		$ 8.999
Subsequent events | Underwriting Agreement
Subsequent events
Issuance of common stock in connection with the 2023 Neurocrine Collaboration Agreement (in shares)		7,777,778
Par value of common stock (in dollars per share)		$ 0.001
Offering price for common stock		$ 8.46
Period for option to exercise additional number of shares	30 days	30 days
Additional number of shares to be issued		1,666,665
Net proceeds received		$ 93,500
Subsequent events | Underwriting Agreement | Pre-Funded Warrants
Subsequent events
Offering price for warrants		$ 8.459
Subsequent events | Underwriting Agreement | Pre-Funded Warrants | Maximum
Subsequent events
Number of warrants issued to purchase common stock		3,333,333

Pay vs Performance Disclosure

Pay vs Performance Disclosure - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pay vs Performance Disclosure
Net Income (Loss)	$ 132,330	$ (46,408)	$ (71,197)

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended
	Dec. 31, 2023
Trading Arrangements, by Individual
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false